Have you ever faced a situation where solving an equation led to the square root of a negative number? Do you know how engineers, physicists, and mathematicians deal with this situation? Yes, this is where Complex Numbers come in! This chapter discusses the idea of Complex numbers and quadratic equations. A complex number has both real and imaginary parts. The imaginary parts are represented by i(iota). Students will carry out basic algebraic operations on complex numbers in the same way as on real numbers, such as addition, subtraction, multiplication, and division. The quadratic equations, or second-degree order equations, teach one how to determine the roots of these equations through the discriminant and quadratic formulas. The primary benefit of using NCERT Solutions for Class 11 Maths is that they offer clear explanations and accurate answers, facilitating a deeper understanding.
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These NCERT solutions for Class 11 deliver step-by-step processes to solve exercises and simplify complicated problems. Many teachers recommend NCERT Solutions because they closely match the exam pattern. In addition to textbook exercises, students are recommended to solve Class 11 Maths Chapter 4 Question Answers to reinforce their learning and ensure they are well-prepared for exams. Through the use of resources such as the NCERT Exemplar, students can solve more complex problems and enhance their knowledge of both complex numbers and quadratic equations. Students need to refer to the NCERT Class 10 Maths books to gain more knowledge. With consistent practice and a clear understanding of these concepts, students can approach both theoretical and applied mathematics confidently. For syllabus, notes, and exemplar solutions, refer to this NCERT article.
Careers360 experts have prepared these NCERT Solutions for Class 11 Maths Chapter 4 to make learning maths easier and help you do better in class and exams. A downloadable PDF is available — click the link below to access it.
Here are the NCERT Class 11 Maths Chapter 4 Complex Numbers and Quadratic Equations question answers with clear, detailed solutions.
Complex Numbers and Quadratic Equations Class 11 Question Answers Exercise: 4.1 Page number: 82-83 Total questions: 14 |
Question 1: Express the given complex number in the form a+ib:
$(5i)(-\frac35 i)$?
Answer:
Given $a+i b:(5 i) \times\left(-\frac{3}{5} i\right)$
$(5 i) \times\left(-\frac{3}{5} i\right)=-\left(5 \times \frac{3}{5}\right)\left(i^2\right)$
$\begin{aligned} & =-3\left(i^2\right) \\ & =3 \end{aligned}$
Question 2: Express each of the complex number in the form $a+ib$.
Answer:
We know that $i^4 = 1$
Now, we will reduce $i^9+i^{19}$ into
$i^9+i^{19}=\left(i^4\right)^2 \cdot i+\left(i^4\right)^3 \cdot i^3$
$= (1)^2.i+(1)^3.(-i)$ $(\because i^4 = 1 , i^3 = -i\ and \ i^2 = -1)$
$=i-i $
$= 0$
Now, in the form of $a+ib$, we can write it as
$0+i0$
Therefore, the answer is $0+i0$.
Question 3: Express each of the complex number in the form a+ib.
$i^{-39}$
Answer:
We know that $i^4 = 1$
Now, we will reduce $i^{-39}$ into
$i^{-39}$ $= (i^{4})^{-9}.i^{-3}$
$= (1)^{-9}.(-i)^{-1}$ $(\because i^4 = 1 , i^3 = -i)$
$= \frac{1}{-i}$
$= \frac{1}{-i} \times \frac{i}{i}$
$= \frac{i}{-i^2}$ $(\because i^2 = -1)$
$= \frac{i}{-(-1)}$
$=i$
Now, in the form of $a+ib$ we can write it as
$0+i1$
Therefore, the answer is $0+i1$.
Question 4: Express each of the complex number in the form a+ib.
$3(7+7i)+i(7+7i)$
Answer:
The given problem is
$3(7+7i)+i(7+7i)$
Now, we will reduce it to
$3(7+7i)+i(7+7i)$ $= 21+21i+7i+7i^2$
$= 21+21i+7i+7(-1)$ $(\because i^2 = -1)$
$= 21+21i+7i-7$
$=14+28i$
Therefore, the answer is $14+28i$
Question 5: Express each of the complex number in the form $a+ib$ .
$(1-i)-(-1+6i)$
Answer:
Given problem is
$(1-i)-(-1+6i)$
Now, we will reduce it to
$(1-i)-(-1+6i)$$=1-i+1-6i$
$= 2-7i$
Therefore, the answer is $2-7i$
Question 6: Express each of the complex number in the form $a+ib$ .
$\left ( \frac{1}{5}+i\frac{2}{5} \right )-\left ( 4+i\frac{5}{2} \right )$
Answer:
Given problem is
$\left ( \frac{1}{5}+i\frac{2}{5} \right )-\left ( 4+i\frac{5}{2} \right )$
Now, we will reduce it to
$\left ( \frac{1}{5}+i\frac{2}{5} \right )-\left ( 4+i\frac{5}{2} \right ) = \frac{1}{5}+i\frac{2}{5}-4-i\frac{5}{2}$
$= \frac{1-20}{5}+i\frac{(4-25)}{10}$
$= -\frac{19}{5}-i\frac{21}{10}$
Therefore, the answer is $-\frac{19}{5}-i\frac{21}{10}$
Question 7: Express each of the complex number in the form $a+ib$ .
$\left [ \left ( \frac{1}{3}+i\frac{7}{3} \right )+\left ( 4+i\frac{1}{3} \right ) \right ]-\left ( -\frac{4}{3}+i \right )$
Answer:
Given problem is
$\left [ \left ( \frac{1}{3}+i\frac{7}{3} \right )+\left ( 4+i\frac{1}{3} \right ) \right ]-\left ( -\frac{4}{3}+i \right )$
Now, we will reduce it into
$\left [ \left ( \frac{1}{3}+i\frac{7}{3} \right )+\left ( 4+i\frac{1}{3} \right ) \right ]-\left ( -\frac{4}{3}+i \right ) = \frac{1}{3}+i\frac{7}{3} + 4+i\frac{1}{3} + \frac{4}{3}-i$
$=\frac{1+4+12}{3}+i\frac{(7+1-3)}{3}$
$=\frac{17}{3}+i\frac{5}{3}$
Therefore, the answer is $\frac{17}{3}+i\frac{5}{3}$
Question 8: Express each of the complex number in the form $a+ib$ .
$(1-i)^4$
Answer:
The given problem is
$(1-i)^4$
Now, we will reduce it to
$(1-i)^4 = ((1-i)^2)^2$
$= (1^2+i^2-2.1.i)^2$ $(using \ (a-b)^2= a^2+b^2-2ab)$
$=(1-1-2i)^2$ $(\because i^2 = -1)$
$= (-2i)^2$
$= 4i^2$
$= -4$
Therefore, the answer is $-4+i0$
Question 9: Express each of the complex number in the form $a+ib$ .
$\left ( \frac{1}{3}+3i \right )^3$
Answer:
Given problem is
$\left ( \frac{1}{3}+3i \right )^3$
Now, we will reduce it to
$\left ( \frac{1}{3}+3i \right )^3=\left ( \frac{1}{3} \right )^3+(3i)^3+3.\left ( \frac{1}{3} \right )^2.3i+3.\frac{1}{3}.(3i)^2$ $(using \ (a+b)^3=a^3+b^3+3a^2b+3ab^2)$
$= \frac{1}{27}+27i^3+i + 9i^2$
$= \frac{1}{27}+27(-i)+i + 9(-1)$ $(\because i^3=-i \ and \ i^2 = -1)$
$=\frac{1}{27}-27i+i-9$
$=\frac{1-243}{27}-26i$
$=-\frac{242}{27}-26i$
Therefore, the answer is
$-\frac{242}{27}-26i$
Question 10: Express each of the complex number in the form $a+ib$ .
$\left ( -2-\frac{1}{3}i \right )^3$
Answer:
Given problem is
$\left ( -2-\frac{1}{3}i \right )^3$
Now, we will reduce it into
$\left ( -2-\frac{1}{3}i \right )^3=-\left ( (2)^3+\left ( \frac{1}{3}i \right )^3 +3.(2)^2\frac{1}{3}i+3.\left ( \frac{1}{3}i \right )^2.2 \right )$ $(using \ (a+b)^3=a^3+b^3+3a^2b+3ab^2)$
$=-\left ( 8+\frac{1}{27}i^3+3.4.\frac{1}{3}i+3.\frac{1}{9}i^2.2 \right )$
$=-\left ( 8+\frac{1}{27}(-i)+4i+\frac{2}{3}(-1) \right )$ $(\because i^3=-i \ and \ i^2 = -1)$
$=-\left ( 8-\frac{1}{27}i+4i-\frac{2}{3} \right )$
$=-\left ( \frac{(-1+108)}{27}i+\frac{24-2}{3} \right )$
$=-\frac{22}{3}-i\frac{107}{27}$
Therefore, the answer is $-\frac{22}{3}-i\frac{107}{27}$
Question 11: Find the multiplicative inverse of each of the complex numbers.
$4-3i$
Answer:
Let $z = 4-3i$
Then,
$\bar z = 4+ 3i$
And
$|z|^2 = 4^2+(-3)^2 = 16+9 =25$
Now, the multiplicative inverse is given by
$z^{-1}= \frac{\bar z}{|z|^2}= \frac{4+3i}{25}= \frac{4}{25}+i\frac{3}{25}$
Therefore, the multiplicative inverse is
$\frac{4}{25}+i\frac{3}{25}$
Question 12: Find the multiplicative inverse of each of the complex numbers.
$\sqrt{5}+3i$
Answer:
Let $z = \sqrt{5}+3i$
Then,
$\bar z = \sqrt{5}-3i$
And
$|z|^2 = (\sqrt5)^2+(3)^2 = 5+9 =14$
Now, the multiplicative inverse is given by
$z^{-1}= \frac{\bar z}{|z|^2}= \frac{\sqrt5-3i}{14}= \frac{\sqrt5}{14}-i\frac{3}{14}$
Therefore, the multiplicative inverse is $\frac{\sqrt5}{14}-i\frac{3}{14}$
Question 13: Find the multiplicative inverse of each of the complex numbers.
$-i$
Answer:
Let $z = -i$
Then,
$\bar z = i$
And
$|z|^2 = (0)^2+(1)^2 = 0+1 =1$
Now, the multiplicative inverse is given by
$z^{-1}= \frac{\bar z}{|z|^2}= \frac{i}{1}= 0+i$
Therefore, the multiplicative inverse is $0+i1$
Question 14: Express the following expression in the form of $a+ib:$
$\frac{(3+i\sqrt{5})(3-i\sqrt{5})}{(\sqrt{3}+\sqrt{2}i)-(\sqrt{3}-i\sqrt{2})}$
Answer:
Given problem is
$\frac{(3+i\sqrt{5})(3-i\sqrt{5})}{(\sqrt{3}+\sqrt{2}i)-(\sqrt{3}-i\sqrt{2})}$
Now, we will reduce it to
$\frac{(3+i\sqrt{5})(3-i\sqrt{5})}{(\sqrt{3}+\sqrt{2}i)-(\sqrt{3}-i\sqrt{2})} = \frac{3^2- (\sqrt5i)^2}{(\sqrt{3}+\sqrt{2}i)-(\sqrt{3}-i\sqrt{2})}$ $(using \ (a-b)(a+b)=a^2-b^2)$
$=\frac{9-5i^2}{\sqrt3+\sqrt2i-\sqrt3+\sqrt2i}$
$=\frac{9-5(-1)}{2\sqrt2i}$ $(\because i^2 = -1)$
$=\frac{14}{2\sqrt2i}\times \frac{\sqrt2i}{\sqrt2i}$
$=\frac{7\sqrt2i}{2i^2}$
$=-\frac{7\sqrt2i}{2}$
Therefore, the answer is $(0-i\frac{7\sqrt2}{2})$
Complex Numbers and Quadratic Equations Class 11 Question Answers Miscellaneous Exercise Page number: 85-86 Total questions: 14 |
Question 1: Evaluate $\left[i^{18}+\left(\frac{1}{i}\right)^{25}\right]^3$ .
Answer:
The given problem is
$\left[i^{18}+\left(\frac{1}{i}\right)^{25}\right]^3$
Now, we will reduce it to
$\left[i^{18}+\left(\frac{1}{i}\right)^{25}\right]^3=\left[\left(i^4\right)^4 \cdot i^2+\frac{1}{\left(i^4\right)^6 \cdot i}\right]^3$
$=\left [ 1^4.(-1)+\frac{1}{1^6.i} \right ]^3$ $(\because i^4 = 1, i^2 = -1 )$
$= \left [ -1+\frac{1}{i} \right ]^3$
$= \left [ -1+\frac{1}{i} \times \frac{i}{i}\right ]^3$
$= \left [ -1+\frac{i}{i^2} \right ]^3$
$= \left [ -1+\frac{i}{-1} \right ]^3 = \left [ -1-i \right ]^3$
Now,
$-(1+i)^3=-(1^3+i^3+3.1^2.i+3.1.i^2)$ $(using \ (a+b)^3=a^3+b^3+3.a^2.b+3.a.b^2)$
$= -(1 - i +3i+3(-1))$ $(\because i^3=-i , i^2 = -1)$
$= -(1 - i +3i-3)= -(-2+2i)$
$=2-2i$
Therefore, the answer is $2-2i$
Answer:
Let two complex numbers be
$z_1=x_1+iy_1$
$z_2=x_2+iy_2$
Now,
$z_1.z_2=(x_1+iy_1).(x_2+iy_2)$
$=x_1x_2+ix_1y_2+iy_1x_2+i^2y_1y_2$
$=x_1x_2+ix_1y_2+iy_1x_2-y_1y_2$ $(\because i^2 = -1)$
$=x_1x_2-y_1y_2+i(x_1y_2+y_1x_2)$
$Re(z_1z_2)= x_1x_2-y_1y_2$
$=Re(z_1z_2)-Im(z_1z_2)$
Hence proved
Answer:
Given problem is
$\small \left ( \frac{1}{1-4i}-\frac{2}{1+i} \right )\left ( \frac{3-4i}{5+i} \right )$
Now, we will reduce it to
$\small \left ( \frac{1}{1-4i}-\frac{2}{1+i} \right )\left ( \frac{3-4i}{5+i} \right ) = \left ( \frac{(1+i)-2(1-4i)}{(1+i)(1-4i)} \right )\left ( \frac{3-4i}{5+i} \right )$
$=\left ( \frac{1+i-2+8i}{1-4i+i-4i^2} \right )\left ( \frac{3-4i}{5+i} \right )$
$=\left ( \frac{-1+9i}{1-3i-4(-1)} \right )\left ( \frac{3-4i}{5+i} \right )$
$=\left ( \frac{-1+9i}{5-3i} \right )\left ( \frac{3-4i}{5+i} \right )$
$=\left ( \frac{-3+4i+27i-36i^2}{25+5i-15i-3i^2} \right )= \left ( \frac{-3+31i+36}{25-10i+3} \right )= \frac{33+31i}{28-10i}= \frac{33+31i}{2(14-5i)}$
Now, multiply numerator and denominator by $(14+5i)$
$\Rightarrow \frac{33+31i}{2(14-5i)}\times \frac{14+5i}{14+5i}$
$\Rightarrow \frac{462+165i+434i+155i^2}{2(14^2-(5i)^2)}$ $(using \ (a-b)(a+b)=a^2-b^2)$
$\Rightarrow \frac{462+599i-155}{2(196-25i^2)}$
$\Rightarrow \frac{307+599i}{2(196+25)}= \frac{307+599i}{2\times 221}= \frac{307+599i}{442}= \frac{307}{442}+i\frac{599}{442}$
Therefore, answer is $\frac{307}{442}+i\frac{599}{442}$
Question 4: If $\small x-iy=\sqrt{\frac{a-ib}{c-id}}$ , prove that $\small (x^2+y^2)^2=\frac{a^2+b^2}{c^2+d^2}.$
Answer:
The given problem is
$\small x-iy=\sqrt{\frac{a-ib}{c-id}}$
Now, multiply the numerator and denominator by
$\sqrt{c+id}$
$x-iy = \sqrt{\frac{a-ib}{c-id}\times \frac{c+id}{c+id}}$
$= \sqrt{\frac{(ac+bd)+i(ad-bc)}{c^2-i^2d^2}}= \sqrt{\frac{(ac+bd)+i(ad-bc)}{c^2+d^2}}$
Now, square both sides
$(x-iy)^2=\left ( \sqrt{\frac{(ac+bd)+i(ad-bc)}{c^2+d^2}} \right )^2$
$=\frac{(ac+bd)+i(ad-bc)}{c^2+d^2}$
$x^2-y^2-2ixy=\frac{(ac+bd)+i(ad-bc)}{c^2+d^2}$
On comparing the real and imaginary parts, we obtain
$x^2-y^2 = \frac{ac+bd}{c^2+d^2} \ \ and \ \ -2xy = \frac{ad-bc}{c^2+d^2} \ \ \ -(i)$
Now,
$(x^2+y^2)^2= (x^2-y^2)^2+4x^2y^2$
$= \left ( \frac{ac+bd}{c^2+d^2} \right )^2+\left ( \frac{ad-bc}{c^2+d^2} \right )^2 \ \ \ \ (using \ (i))$
$=\frac{a^2c^2+b^2d^2+2acbd+a^2d^2+b^2c^2-2adbc}{(c^2+d^2)^2}$
$=\frac{a^2c^2+b^2d^2+a^2d^2+b^2c^2}{(c^2+d^2)^2}$
$=\frac{a^2(c^2+d^2)+b^2(c^2+d^2)}{(c^2+d^2)^2}$
$=\frac{(a^2+b^2)(c^2+d^2)}{(c^2+d^2)^2}$
$=\frac{(a^2+b^2)}{(c^2+d^2)}$
Hence proved.
Question 5: If $\small z_1=2-i, z_2=1+i$ , find $\small \left |\frac{z_1+z_2+1}{z_1-z_2+1} \right |$ .
Answer:
It is given that
$\small z_1=2-i, z_2=1+i$
Then,
$\small \left |\frac{z_1+z_2+1}{z_1-z_2+1} \right | =\left | \frac{2-i+1+i+1}{2-i-1-i+1} \right | = \left | \frac{4}{2(1-i)} \right |= \left | \frac{2}{(1-i)} \right |$
Now, multiply the numerator and denominator by $1+i$
$\Rightarrow \left | \frac{2}{(1-i)} \times \frac{1+i}{1+i} \right |=\left |\frac{2(1+i)}{1^2-i^2} \right |=\left | \frac{2(1+i)}{1+1} \right |= \left| 1+i \right |$
Now,
$|1+i| = \sqrt{1^2+1^2}=\sqrt{1+1}=\sqrt{2}$
Therefore, the value of
$\small \left |\frac{z_1+z_2+1}{z_1-z_2+1} \right |$ is $\sqrt{2}$
Question 6: If $\small a+ib=\frac{(x+i)^2}{2x^2+1}$ , prove that $\small a^2+b^2=\frac{(x^2+1)^2}{(2x^2+1)^2}$ .
Answer:
It is given that
$\small a+ib=\frac{(x+i)^2}{2x^2+1}$
Now, we will reduce it to
$\small a+ib=\frac{(x+i)^2}{2x^2+1} = \frac{x^2+i^2+2xi}{2x^2+1}=\frac{x^2-1+2xi}{2x^2+1}=\frac{x^2-1}{2x^2+1}+i\frac{2x}{2x^2+1}$
On comparing the real and imaginary parts, we will get
$a=\frac{x^2-1}{2x^2+1}\ and \ b=\frac{2x}{2x^2+1}$
Now,
$a^2+b^2=\left ( \frac{x^2-1}{2x^2+1} \right )^2+\left ( \frac{2x}{2x^2+1} \right )^2$
$= \frac{x^4+1-2x^2+4x^2}{(2x^2+1)^2}$
$= \frac{x^4+1+2x^2}{(2x^2+1)^2}$
$= \frac{(x^2+1)^2}{(2x^2+1)^2}$
Hence proved
Question 7 (i): Let $\small z_1=2-i,z_2=-2+i.$ Find
$\small Re\left ( \frac{z_1z_2}{\bar{z_1}} \right )$
Answer:
It is given that
$\small z_1=2-i \ and \ z_2=-2+i$
Now,
$z_1z_2= (2-i)(-2+i)= -4+2i+2i-i^2=-4+4i+1= -3+4i$
And
$\bar z_1 = 2+i$
Now,
$\frac{z_1z_2}{\bar z_1}= \frac{-3+4i}{2+i}= \frac{-3+4i}{2+i}\times \frac{2-i}{2-i}= \frac{-6+3i+8i-4i^2}{2^2-i^2}= \frac{-6+11i+4}{4+1}$ $= \frac{-2+11i}{5}= -\frac{2}{5}+i\frac{11}{5}$
Now,
$Re\left ( \frac{z_1z_2}{z_1} \right )= -\frac{2}{5}$
Therefore, the answer is
$-\frac{2}{5}$
Question 7 (ii): Let $\small z_1=2-i,z_2=-2+i.$ Find
$\small Im\left ( \frac{1}{z_1\bar{z_1}} \right )$
Answer:
It is given that
$z_1= 2-i$
Therefore,
$\bar z_1= 2+i$
NOw,
$z_1\bar z_1= (2-i)(2+i)= 2^2-i^2=4+1=5$ $(using \ (a-b)(a+b)= a^2-b^2)$
Now,
$\frac{1}{z_1\bar z_1}= \frac{1}{5}$
Therefore,
$Im\left ( \frac{1}{z_1\bar z_1} \right )= 0$
Therefore, the answer is 0.
Question 8: Find the real numbers x and y if $\small (x-iy)(3+5i)$ is the conjugate of $\small -6-24i$.
Answer:
Let
$z = \small (x-iy)(3+5i) = 3x+5xi-3yi-5yi^2= 3x+5y+i(5x-3y)$
Therefore,
$\bar z = (3x+5y)-i(5x-3y) \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ -(i)$
Now, it is given that
$\bar z = -6-24i \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ -(ii)$
Comparing (i) and (ii), we will get
$(3x+5y)-i(5x-3y) = -6-24i$
On comparing the real and imaginary parts, we will get
$3x+5y=-6 \ \ \ and \ \ \ 5x-3y = 24$
On solving these, we will get
$x = 3 \ \ \ and \ \ \ y =- 3$
Therefore, the values of x and y are 3 and -3, respectively
Question 9: Find the modulus of $\small \frac{1+i}{1-i}-\frac{1-i}{1+i}$ .
Answer:
Let
$z =\small \frac{1+i}{1-i}-\frac{1-i}{1+i}$
Now, we will reduce it to
$z =\small \frac{1+i}{1-i}-\frac{1-i}{1+i} = \frac{(1+i)^2-(1-i)^2}{(1+i)(1-i)}= \frac{1^2+i^2+2i-1^2-i^2+2i}{1^2-i^2}$ $= \frac{4i}{1+1}= \frac{4i}{2}=2i$
Now,
$r\cos\theta = 0 \ \ and \ \ r\sin \theta = 2$
Square and add both sides, we will get,
$r^2\cos^2\theta+r^2\sin^2 \theta = 0^2+2^2$
$r^2(\cos^2\theta+\sin^2 \theta) = 4$
$r^2 = 4 \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\because \cos^2\theta+\sin^2 \theta = 1)$
$r = 2 \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\because r > 0)$
Therefore, the modulus of
$\small \frac{1+i}{1-i}-\frac{1-i}{1+i}$ is 2
Question 10: If $\small (x+iy)^3=u+iv$ , then show that $\small \frac{u}{x}+\frac{v}{y}=4 (x^2-y^2).$
Answer:
it is given that
$\small (x+iy)^3=u+iv$
Now, expand the Left-hand side
$x^3+(iy)^3+3.(x)^2.iy+3.x.(iy)^2= u + iv$
$x^3+i^3y^3+3x^2iy+3xi^2y^2= u + iv$
$x^3-iy^3+3x^2iy-3xy^2= u + iv$ $(\because i^3 = -i \ \ and \ \ i^2 = -1)$
$x^3-3xy^2+i(3x^2y-y^3)= u + iv$
On comparing the real and imaginary parts, we will get,
$u = x^3-3xy^2 \ \ \ and \ \ \ v = 3x^2y-y^3$
Now,
$\frac{u}{x}+\frac{v}{y}= \frac{x(x^2-3y^2)}{x}+\frac{y(3x^2-y^2)}{y}$
$= x^2-3y^2+3x^2-y^2$
$= 4x^2-4y^2$
$= 4(x^2-y^2)$
Hence proved
Answer:
Let
$\alpha = a+ib$ and $\beta = x+iy$
It is given that
$\small |\beta|=1\Rightarrow \sqrt{x^2+y^2} = 1\Rightarrow x^2+y^2 = 1$
and
$\small \bar \alpha = a-ib$
Now,
$\small \left | \frac{\beta -\alpha }{1-\bar{\alpha }\beta } \right | = \left | \frac{(x+iy)-(a+ib)}{1-(a-ib)(x+iy)} \right | = \left | \frac{(x-a)+i(y-b)}{1-(ax+iay-ibx-i^2yb)} \right |$
$\small = \left | \frac{(x-a)+i(y-b)}{(1-ax-yb)-i(bx-ay)} \right |$
$\small = \frac{\sqrt{(x-a)^2+(y-b)^2}}{\sqrt{(1-ax-yb)^2+(bx-ay)^2}}$
$\small = \frac{\sqrt{x^2+a^2-2xa+y^2+b^2-yb}}{\sqrt{1+a^2x^2+b^2y^2-2ax+2abxy-by+b^2x^2+a^2y^2-2abxy}}$
$\small = \frac{\sqrt{(x^2+y^2)+a^2-2xa+b^2-yb}}{\sqrt{1+a^2(x^2+y^2)+b^2(x^2+y^2)-2ax+2abxy-by-2abxy}}$
$\small = \frac{\sqrt{1+a^2-2xa+b^2-yb}}{\sqrt{1+a^2+b^2-2ax-by}}$ $\small (\because x^2+y^2 = 1 \ given)$
$\small =1$
Therefore, value of $\small \left | \frac{\beta -\alpha }{1-\bar{\alpha }\beta } \right |$ is 1
Question 12: Find the number of non-zero integral solutions of the equation $\small |1-i|^x=2^x$.
Answer:
Given problem is
$\small |1-i|^x=2^x$
Now,
$( \sqrt{1^2+(-1)^2 })^x=2^x$
$( \sqrt{1+1 })^x=2^x$
$\left ( \sqrt{2 }\right )^x=2^x$
$2^{\frac{x}{2}}= 2^x$
$\frac{x}{2}=x$
$\frac{x}{2}=0$
x = 0 is the only possible solution to the given problem
Therefore, there is 0 number of non-zero integral solution of the equation $\small |1-i|^x=2^x$
Question 13: If $\small (a+ib)(c+id)(e+if)(g+ih)=A+iB,$ then show that $\small (a^2+b^2)(c^2+d^2)(e^2+f^2)(g^2+h^2)=A^2+B^2$
Answer:
It is given that
$\small (a+ib)(c+id)(e+if)(g+ih)=A+iB,$
Now, take the modulus on both sides
$\left | (a+ib)(c+id)(e+if)(g+ih) \right |= \left | A+iB \right |$
$|(a+ib)||(c+id)||(e+if)||(g+ih)|= \left | A+iB \right |$ $(\because |z_1z_2|=|z_1||z_2|)$
$(\sqrt{a^2+b^2})(\sqrt{c^2+d^2})(\sqrt{e^2+f^2})(\sqrt{g^2+h^2})= (\sqrt{A^2+B^2})$
Square both sides, we will get
$({a^2+b^2})({c^2+d^2})({e^2+f^2})({g^2+h^2})= (A^2+B^2)$
Hence proved
Question 14: If $\small \left ( \frac{1+i}{1-i} \right )^m=1,$ then find the least positive integral value of $\small m$ .
Answer:
Let
$z = \left ( \frac{1+i}{1-i} \right )^m$
Now, multiply both numerator and denominator by $(1+i)$
We will get,
$z = \left ( \frac{1+i}{1-i}\times \frac{1+i}{1+i} \right )^m$
$= \left ( \frac{(1+i)^2}{1^2-i^2} \right )^m$
$= \left ( \frac{1^2+i^2+2i}{1+1} \right )^m$
$= \left ( \frac{1-1+2i}{2} \right )^m$ $(\because i^2 = -1)$
$= \left ( \frac{2i}{2} \right )^m$
$= i^m$
We know that $i^4 = 1$
Therefore, the least positive integral value of $\small m$ is 4.
Exercise-wise NCERT Solutions of Complex Numbers and Quadratic Equations Class 11 Maths Chapter 4 are provided in the links below.
Question:
If $\alpha$ is a root of the equation $x^2+x+1=0$ and $\sum_{\mathrm{k}=1}^{\mathrm{n}}\left(\alpha^{\mathrm{k}}+\frac{1}{\alpha^{\mathrm{k}}}\right)^2=20$, then n is equal to ______
Solution:
We have,
$\begin{aligned}
& \alpha=\omega \\
& \therefore\left(\omega^{\mathrm{k}}+\frac{1}{\omega^{\mathrm{k}}}\right)^2=\omega^{2 \mathrm{k}}+\frac{1}{\omega^{2 \mathrm{k}}}+2 \\
& =\omega^{2 \mathrm{k}}+\omega^{\mathrm{k}}+2 \quad \because \omega^{3 \mathrm{k}}=1
\end{aligned}$
$\begin{aligned}
& \therefore \sum_{k=1}^n\left(\omega^{2 k}+\omega^k+2\right)=20 \\
& \Rightarrow\left(\omega^2+\omega^4+\omega^6+\ldots+\omega^{2 n}\right)+\left(\omega+\omega^2+\omega^3+\ldots+\right. \\
& \left.\omega^n\right)+2 n=20
\end{aligned}$
Now if $n=3 m, \quad m \in I$
Then $0+0+2 \mathrm{n}=20 \Rightarrow \mathrm{n}=10$ (not satisfy) if $n=3 m+1$, then
$\begin{aligned}
& \omega^2+\omega+2 n=20 \\
& -1+2 n=20 \Rightarrow n=\frac{21}{2} \text { (not possible) } \\
& \text { if } n=3 m+2, \\
& \left(\omega^8+\omega^{10}\right)+\left(\omega^4+\omega^5\right)+2 n=20 \\
& \Rightarrow\left(\omega^2+\omega\right)+\left(\omega+\omega^2\right)+2 n=20 \\
& 2 n=22
\end{aligned}$
$\begin{aligned} & \mathrm{n}=11 \text { satisfy } \mathrm{n}=3 \mathrm{~m}+2 \\ & \therefore \mathrm{n}=11\end{aligned}$
Hence, the correct answer is 11.
Topics you will learn in NCERT Class 11 Maths Chapter 4 Complex Numbers and Quadratic Equations include:
A complex number is expressed as a + bi, where 'a' and 'b' are real numbers, and 'i' is the imaginary unit.
Imaginary Numbers: The square root of a negative real number is called an imaginary number, represented as √−1 = i
Equality of Complex Number: Two complex numbers z1 = x1 + iy1 and z2 = x2 + iy2 are equal if x1 = x2 and y1 = y2.
1. Addition: $\quad \mathrm{z}_1+\mathrm{z}_2=\left(\mathrm{x}_1+\mathrm{x}_2\right)+\mathrm{i}\left(\mathrm{y}_1+\mathrm{y}_2\right)$
2. Subtraction: $\quad \mathrm{z}_1-\mathrm{z}_2=\left(\mathrm{x}_1-\mathrm{x}_2\right)+\mathrm{i}\left(\mathrm{y}_1-\mathrm{y}_2\right)$
3. Multiplication: $\quad \mathrm{z}_1 \times \mathrm{z}_2=\left(\mathrm{x}_1 \mathrm{x}_2-\mathrm{y}_1 \mathrm{y}_2\right)+\mathrm{i}\left(\mathrm{x}_1 \mathrm{y}_2+\mathrm{x}_2 \mathrm{y}_1\right)$
4. Division: $\left(z_2 \neq 0\right) \quad \frac{z_1}{z_2}=\frac{\left(\mathbf{x}_1 \mathbf{x}_2+\mathbf{y}_1 \mathbf{y}_2\right)+i\left(\mathbf{y}_1 \mathbf{x}_2-\mathbf{x}_1 \mathbf{y}_2\right)}{\mathbf{x}_2^2+\mathbf{y}_2^2}$
Conjugate of Complex Number: The conjugate of a complex number z = x + iy is represented as z̅ = x - iy.
Modulus of a Complex Number: |z| = $\sqrt{x_2+y_2}$
Argument of a Complex Number: The angle made by the line joining the point z to the origin, with the positive X-axis in an anti-clockwise sense, is called the argument (arg) of the complex number.
When x > 0 and y > 0 ⇒ arg(z) = θ
When x < 0 and y > 0 ⇒ arg(z) = π - θ
When x < 0 and y < 0 ⇒ arg(z) = -(π - θ)
When x > 0 and y < 0 ⇒ arg(z) = -θ
z = |z| (cosθ + isinθ), where θ = arg(z).
The general polar form of z is:
$z=|z|[\cos (\theta+2 n \pi)+i \sin (\theta+2 n \pi)]$, where n is an integer.
Here are some approaches that students can use to solve complex numbers and quadratic equation problems.
For JEE aspirants, it is important to go beyond NCERT. Below are some extra topics that can help you build a deeper understanding and handle challenging problems with confidence.
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We at Careers360 compiled all the NCERT class 11 Maths solutions in one place for easy student reference. The following links will allow you to access them.
Also, read,
Given below are the subject-wise NCERT solutions of class 11 NCERT:
NCERT solutions for class 11 biology |
NCERT solutions for class 11 chemistry |
NCERT solutions for class 11 physics |
Here are some useful links for NCERT books and the NCERT syllabus for class 11:
Frequently Asked Questions (FAQs)
A complex number is of the form z = a + ib, where a is the real part, b is the imaginary part, and the value of the square of i is –1.
It is z = |z|(cos θ+i sin θ), where |z| is the modulus and θ is the argument.
This chapter covers topics such as:
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Many trusted educational websites, such as Careers360, offer free downloadable PDFS of the NCERT Solutions for class 11 Maths. Careers360 provides step-by-step explanations for all textbook exercises, helping students understand concepts clearly and prepare effectively for exams.
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