Skip to main contentSkip to solution

If A=[1−12−1],B=[x1y−1]A = \begin{bmatrix}1 & -1\\2 & -1\end{bmatrix}, B = \begin{bmatrix}x & 1\\y & -1\end{bmatrix} and (A+B)2=A2+B2(A+B)^2 = A^2 + B^2, then which of the following are correct?

A. x=1x=1

B. x=4x=4

C. y=1y=1

D. y=4y=4

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

Expanding (A+B)2=A2+B2(A+B)^2 = A^2+B^2 requires AB+BA=0AB + BA = 0.

Computing, AB=[x−y22x−y3]AB = \begin{bmatrix}x-y&2\\2x-y&3\end{bmatrix} and BA=[x+2−x−1y−21−y]BA = \begin{bmatrix}x+2&-x-1\\y-2&1-y\end{bmatrix}.

Setting the sum to zero gives 1−x=01-x=0 and 4−y=04-y=0, so x=1x=1 and y=4y=4.

Keyboard Shortcuts

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