RD Sharma Class 12 Exercise 7.2 Simultaneous Linear Equation Solutions Maths - Download PDF Free Online
RD Sharma Class 12 Exercise 7.2 Simultaneous Linear Equation Solutions Maths - Download PDF Free Online
Updated on 20 Jan 2022, 03:26 PM IST
RD Sharma Class 12 Solutions Chapter 7 Exercise 7.2 (Solution of Simultaneous Linear Equations) consists of problems on finding the homogeneous system of linear equations. These problems are solved by CAREER360 experts in a basic manner to accelerate the test readiness of students. It essentially helps during the update and further develops certainty among understudies before showing up for the board test.
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RD Sharma Class 12 Solutions Chapter 7 Solution of Simultaneous Linear Equation - Other Exercise
Solution of simultaneous linear equations Excercise: 7.2
Answer: $x=y=z=0$ Hint: If $\left | A \right |\neq 0$, then $x=y=z=0$ is the only solution of the homogeneous system. Given: $2x-y+z=0$ $3x+2y-z=0$ $x+4y+3z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 2 & -1 &1 \\ 3& 2 &-1 \\ 1& 4 &3 \end{bmatrix}\begin{bmatrix} x\\ y\\ z\end{bmatrix} = \begin{bmatrix} 0\\ 0\\ 0\end{bmatrix}$ $A= \begin{bmatrix} 2 & -1 &1 \\ 3& 2& -1\\ 1& 4 & 3 \end{bmatrix}$ Let $A= \begin{vmatrix} 2 & -1 &1 \\ 3& 2& -1\\ 1& 4 & 3 \end{vmatrix}$ $=2(6+4)+1(9+1)+1(12-2)$ $=20+10+10$ $=40$ $\left | A \right |\neq 0$ So the given system of equations has a trivial solution. $x=0, y=0, z=0$
Answer: $x=\frac{-5k}{11}, y=\frac{12k}{11}, z=k$ Hint: If $\left | A \right |= 0$, then the system of equation has non-trivial solution. Given: $2x-y+2z=0$ $5x+3y-z=0$ $x+5y-5z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 2& -1& 2\\ 5 & 3& -1\\ 1& 5& -5 \end{bmatrix}\begin{bmatrix} x\\ y\\ z\end{bmatrix}=\begin{bmatrix} 0\\ 0\\ 0\end{bmatrix}$ Let $A=\begin{bmatrix} 2& -1& 2\\ 5 & 3& -1\\ 1& 5& -5 \end{bmatrix},X=\begin{bmatrix} x\\ y\\ z\end{bmatrix},B=\begin{bmatrix} 0\\ 0\\ 0\end{bmatrix}$ i.e. $AX=B$ $\left | A \right |=\begin{vmatrix} 2& -1& 2\\ 5 & 3& -1\\ 1& 5& -5 \end{vmatrix}$ $=2(-15+5)+1(-25+1)+2(25-3)$ $=-20-24+ 44$ $=0$ So, the given system has non-trivial solution. To find the solutions we write $2x-y=-2z$ $5x+3y=z$ let $z=k$ $\begin{bmatrix} 2 &-1 \\ 5 & 3 \end{bmatrix}\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} -2k\\ k\end{bmatrix}$
$\left | A \right |=\begin{vmatrix} 2 &-1 \\ 5 & 3 \end{vmatrix}=11\neq 0$ So A-1 exists $adjA=\begin{bmatrix} 3 & 1\\ -5 & 2\end{bmatrix}$ $A^{-1}=\frac{1}{\left | A \right |}adjA$ $A^{-1}=\frac{1}{11}\begin{bmatrix} 3 & 1\\ -5 &2 \end{bmatrix}$ Now, $X=A^{-1}B$ $\begin{bmatrix} x\\ y\end{bmatrix}=\frac{1}{11}\begin{bmatrix} 3 & 1\\ -5 &2 \end{bmatrix}\begin{bmatrix} -2k\\ k\end{bmatrix}$ $=\frac{1}{11}\begin{bmatrix} -5k\\ 12k\end{bmatrix}$ $x=\frac{-5k}{11},y=\frac{12k}{11}$ x,z and y satisfy the third equation $\frac{-5k}{11}+5\left ( \frac{12k}{11} \right )-5z=0$ $5z=\frac{55k}{11}$ $z=k$
Hence $x=\frac{-5k}{11}, y=\frac{12k}{11}, z=k$, where $k\in R$
Answer: $x= \frac{-9k}{13},y= \frac{-k}{13},z= k$ Hint: If $\left | A \right |= 0$, then the system of equation has non-trivial solution. Given: $3x-y+2z=0$ $4x+3y+3z=0$ $5x+7y+4z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 3 & -1 & 2\\ 4& 3 & 3\\ 5& 7 & 4 \end{bmatrix}\begin{bmatrix} x\\ y\\ z \end{bmatrix}=\begin{bmatrix} 0\\ 0\\0 \end{bmatrix}$ $A=\begin{bmatrix} 3 & -1 & 2\\ 4& 3 & 3\\ 5& 7 & 4 \end{bmatrix}$ let $\left | A \right |=\begin{vmatrix} 3 & -1 & 2\\ 4& 3 & 3\\ 5& 7 & 4 \end{vmatrix}$ $= 3(12-21)+1(16-15)+2(28-15)$ $= -27+1+26$ $= 0$ So, the given system of equation has a non-trivial solution. To find these solutions, we write the first two equations as $3x-y=-2z$ $4x+3y=-3z$ Let $z=k$, then we have $\begin{bmatrix} 3 & -1\\ 4 & 3\end{bmatrix}\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} -2k\\ -3k\end{bmatrix}$ $A=\begin{bmatrix} 3 & -1\\ 4 & 3\end{bmatrix},X=\begin{bmatrix} x\\ y\end{bmatrix},B=\begin{bmatrix} -2k\\ -3k\end{bmatrix}$ Where, $\left | A \right |=\begin{vmatrix} 3 & -1\\ 4 & 3\end{vmatrix}=13\neq 0$ So $A^{-1}$ exists $adjA=\begin{bmatrix} 3 & 1\\ -4 & 3\end{bmatrix}$ $A^{-1}=\frac{1}{\left | A \right |}adjA$ $A^{-1}=\frac{1}{13}\begin{bmatrix} 3 & 1\\ -4& 3\end{bmatrix}$ Now, $X=A^{-1}B$ $\begin{bmatrix} x\\ y\end{bmatrix}=\frac{1}{13}\begin{bmatrix} 3 & 1\\ -4& 3\end{bmatrix}\begin{bmatrix} -2k\\ -3k\end{bmatrix}$ $=\frac{1}{13}\begin{bmatrix} -9k\\ -k\end{bmatrix}$ $x=\frac{-9k}{13}, y=\frac{-k}{13}$ Put in third equation, it satisfies it too. Hence $x=\frac{-9k}{13}, y=\frac{-k}{13},z=k$, where $k\in R$
Answer: $x= 2k,y= 4k,z= k$ Hint: If $\left | A \right |= 0$, then the system of equation has non-trivial solution. Given: $x+y-6z=0$ $x-y+2z=0$ $-3x+y+2z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 1 & 1 & -6\\ 1& -1 & 2\\ -3& 1 & 2 \end{bmatrix}\begin{bmatrix} x\\ y\\ z \end{bmatrix}=\begin{bmatrix} 0\\ 0\\0 \end{bmatrix}$ $A=\begin{bmatrix} 1 & 1 & -6\\ 1& -1 & 2\\ -3& 1 & 2 \end{bmatrix}$ let $\left | A \right |=\begin{vmatrix} 1 & 1 & -6\\ 1& -1 & 2\\ -3& 1 & 2 \end{vmatrix}$ $= 1(-2-2)-1(2+6)-6(1-3)$ $= -4-8+12$ $= 0$ So, the given system of equation has a non-trivial solution. To find these solutions, we write the first two equations as $x+y=6z$ $x-y=-2z$ Let $z=k$, then we have $\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix}\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} 6k\\ -2k\end{bmatrix}$ $A=\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix},X=\begin{bmatrix} x\\ y\end{bmatrix},B=\begin{bmatrix} 6k\\ -2k\end{bmatrix}$ Where, $\left | A \right |=\begin{vmatrix} 1 & 1\\ 1 & -1\end{vmatrix}=-2\neq 0$ So $A^{-1}$ exists $adjA=\begin{bmatrix} -1 & -1\\ -1 & 1\end{bmatrix}$ $A^{-1}=\frac{1}{\left | A \right |}adjA$ $A^{-1}=\frac{1}{-2}\begin{bmatrix} -1 & -1\\ -1& 1\end{bmatrix}$ Now, $X=A^{-1}B$ $\begin{bmatrix} x\\ y\end{bmatrix}=\frac{1}{-2}\begin{bmatrix} -1 & -1\\ -1& 1\end{bmatrix}\begin{bmatrix} 6k\\ -2k\end{bmatrix}$ $\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} 2k\\ 4k\end{bmatrix}$ $x=2k, y=4k$ Put in third equation, so these values$x=2k, y=4k,z=k$satisfies it. Hence ,$x=2k, y=4k,z=k$, where $k\in R$
Answer: $x= 2k,y= -3k,z= k$ Hint: If $\left | A \right |= 0$, then the system of equation has non-trivial solution. Given: $x+y+z=0$ $x-y-5z=0$ $x+2y+4z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 1 & 1 & 1\\ 1& -1 & -5\\ 1& 2 & 4\end{bmatrix}\begin{bmatrix} x\\ y\\ z \end{bmatrix}=\begin{bmatrix} 0\\ 0\\0 \end{bmatrix}$ $A=\begin{bmatrix} 1 & 1 & 1\\ 1& -1 & -5\\ 1& 2& 4 \end{bmatrix}$ let $\left | A \right |=\begin{vmatrix} 1 & 1 & 1\\ 1& -1 & -5\\ 1& 2 & 4 \end{vmatrix}$ $= 1(-4+10)-1(4+5)+1(2+1)$ $= 6-9+3$ $= 0$ So, the given system of equation has a non-trivial solution. To find these solutions, we write the first two equations as $x+y=6z$ $x-y=-2z$ Let $z=k$, then we have $\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix}\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} -k\\ 5k\end{bmatrix}$ $A=\begin{bmatrix} 1 & 1\\ 1 & -1\end{bmatrix},X=\begin{bmatrix} x\\ y\end{bmatrix},B=\begin{bmatrix} -k\\ -5k\end{bmatrix}$ Where, $\left | A \right |=\begin{vmatrix} 1 & 1\\ 1 & -1\end{vmatrix}=-2\neq 0$ So $A^{-1}$ exists $adjA=\begin{bmatrix} -1 & -1\\ -1 & 1\end{bmatrix}$ $A^{-1}=\frac{1}{\left | A \right |}adjA$ $A^{-1}=\frac{1}{-2}\begin{bmatrix} -1 & -1\\ -1& 1\end{bmatrix}$ Now, $X=A^{-1}B$ $\begin{bmatrix} x\\ y\end{bmatrix}=\frac{1}{-2}\begin{bmatrix} -1 & -1\\ -1& 1\end{bmatrix}\begin{bmatrix} -k\\ 5k\end{bmatrix}$ $\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} 2k\\ -3k\end{bmatrix}$ $x=2k, y=-3k$ Put in third equation, so these values$x=2k, y=-3k,z=k$satisfies it. Hence ,$x=2k, y=-3k,z=k$, where $k\in R$
Answer: $x= \frac{k}{3},y= \frac{2k}{3},z= k$ Hint: If $\left | A \right |= 0$, then the system of equation has non-trivial solution. Given: $x+y-z=0$ $x-2y+z=0$ $3x+6y-5z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 1 & 1 & -1\\ 1& -2 & 1\\ 3& 6 & -5 \end{bmatrix}\begin{bmatrix} x\\ y\\ z \end{bmatrix}=\begin{bmatrix} 0\\ 0\\0 \end{bmatrix}$ $A=\begin{bmatrix} 1 & 1 & -1\\ 1& -2 & 1\\ 3& 6 & -5 \end{bmatrix}$ let $\left | A \right |=\begin{vmatrix} 1 & 1 & -1\\ 1& -2 & 1\\ 3& 6 & -5 \end{vmatrix}$ $= 1(10-6)-1(-5-3)-1(6+6)$ $= 4+8-12$ $= 0$ So, the given system of equation has a non-trivial solution. To find these solutions, we write the first two equations as $x+y=z$ $x-2y=-z$ Let $z=k$, then we have $\begin{bmatrix} 1 & 1\\ 1 & -2\end{bmatrix}\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} k\\ -k\end{bmatrix}$ $A=\begin{bmatrix} 1 & 1\\ 1 & -2\end{bmatrix},X=\begin{bmatrix} x\\ y\end{bmatrix},B=\begin{bmatrix} k\\ -k\end{bmatrix}$ Where, $\left | A \right |=\begin{vmatrix} 1 & 1\\ 1 & -2\end{vmatrix}=-3\neq 0$ So $A^{-1}$ exists $adjA=\begin{bmatrix} -2 & -1\\ -1 & 1\end{bmatrix}$ $A^{-1}=\frac{1}{\left | A \right |}adjA$ $A^{-1}=\frac{1}{-3}\begin{bmatrix} -2 & -1\\ -1& 1\end{bmatrix}$ Now, $X=A^{-1}B$ $\begin{bmatrix} x\\ y\end{bmatrix}=\frac{1}{-3}\begin{bmatrix} -2 & -1\\ -1& 1\end{bmatrix}\begin{bmatrix} k\\ -k\end{bmatrix}$ $\begin{bmatrix} x\\ y\end{bmatrix}=\begin{bmatrix} \frac{k}{3}\\ \frac{2k}{3} \end{bmatrix}$ $x=\frac{k}{3}, y=\frac{2k}{3}$ Put in third equation, so these values$x=\frac{k}{3}, y=\frac{2k}{3},z=k$ satisfies it. Hence ,$x=\frac{k}{3}, y=\frac{2k}{3},z=k$ where $k\in R$
Answer: $x=y=z=0$ Hint: If $\left | A \right |\neq 0$, then $x=y=z=0$ Given: $2x+3y-z=0$ $x-y-2z=0$ $3x+y+3z=0$ Explanation: The given homogeneous system can be written in matrix form i.e. $\begin{bmatrix} 2 & 3 &-1 \\ 1& -1 &-2 \\ 3& 1 &3 \end{bmatrix}\begin{bmatrix} x\\ y\\ z\end{bmatrix} = \begin{bmatrix} 0\\ 0\\ 0\end{bmatrix}$ $A=\begin{bmatrix} 2 & 3 &-1 \\ 1& -1 &-2 \\ 3& 1 &3 \end{bmatrix}$ Let $\left | A \right |=\begin{vmatrix} 2 & 3 &-1 \\ 1& -1 &-2 \\ 3& 1 &3 \end{vmatrix}$ $=2(-3+2)-3(3+6)-1(1+3)$ $=-2-27-4$ $=-33$ $\left | A \right |\neq 0$ Hence, $x=y=z=0$
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Sums in matrix method for homogeneous system.
Sums in non-singular coefficient matrix of linear equations
Not just these, all the concepts that are asked in the class 12 mathematics textbook are covered here. This is a one-stop solution that could help the students in all means.
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