Skip to main contentSkip to solution

Let A be a square matrix of order 2 such that [2132]A[−325−3]=[1001]\begin{bmatrix} 2 & 1 \\ 3 & 2 \end{bmatrix} A \begin{bmatrix} -3 & 2 \\ 5 & -3 \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}, then A is:

Solution

✅ Correct Option: 3

Given the equation:

[2132]A[−325−3]=[1001]\begin{bmatrix} 2 & 1 \\ 3 & 2 \end{bmatrix} A \begin{bmatrix} -3 & 2 \\ 5 & -3 \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}

Let P=[2132]P = \begin{bmatrix} 2 & 1 \\ 3 & 2 \end{bmatrix}, Q=[−325−3]Q = \begin{bmatrix} -3 & 2 \\ 5 & -3 \end{bmatrix}, and I=[1001]I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}

The equation becomes: PAQ=IPAQ = I


To isolate AA, multiply both sides on the left by P−1P^{-1} and on the right by Q−1Q^{-1}:

P−1(PAQ)Q−1=P−1IQ−1P^{-1}(PAQ)Q^{-1} = P^{-1}IQ^{-1}

A=P−1Q−1A = P^{-1}Q^{-1}


For matrix P=[2132]P = \begin{bmatrix} 2 & 1 \\ 3 & 2 \end{bmatrix}:

det(P)=(2)(2)−(1)(3)\text{det}(P) = (2)(2) - (1)(3)

=4−3= 4 - 3

=1= 1

Using the inverse formula for a 2×2 matrix:

P−1=11[2−1−32]P^{-1} = \frac{1}{1}\begin{bmatrix} 2 & -1 \\ -3 & 2 \end{bmatrix}

=[2−1−32]= \begin{bmatrix} 2 & -1 \\ -3 & 2 \end{bmatrix}


For matrix Q=[−325−3]Q = \begin{bmatrix} -3 & 2 \\ 5 & -3 \end{bmatrix}:

det(Q)=(−3)(−3)−(2)(5)\text{det}(Q) = (-3)(-3) - (2)(5)

=9−10= 9 - 10

=−1= -1

Q−1=1−1[−3−2−5−3]Q^{-1} = \frac{1}{-1}\begin{bmatrix} -3 & -2 \\ -5 & -3 \end{bmatrix}

=[3253]= \begin{bmatrix} 3 & 2 \\ 5 & 3 \end{bmatrix}


A=P−1Q−1A = P^{-1}Q^{-1}

=[2−1−32][3253]= \begin{bmatrix} 2 & -1 \\ -3 & 2 \end{bmatrix}\begin{bmatrix} 3 & 2 \\ 5 & 3 \end{bmatrix}

First row, first column: (2)(3)+(−1)(5)=6−5=1(2)(3) + (-1)(5) = 6 - 5 = 1

First row, second column: (2)(2)+(−1)(3)=4−3=1(2)(2) + (-1)(3) = 4 - 3 = 1

Second row, first column: (−3)(3)+(2)(5)=−9+10=1(-3)(3) + (2)(5) = -9 + 10 = 1

Second row, second column: (−3)(2)+(2)(3)=−6+6=0(-3)(2) + (2)(3) = -6 + 6 = 0

A=[1110]A = \begin{bmatrix} 1 & 1 \\ 1 & 0 \end{bmatrix}

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question