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If (AB)T=C(AB)^T = C, where A=[x−123]A = \begin{bmatrix} x & -1 \\ 2 & 3 \end{bmatrix}, B=[451−2]B = \begin{bmatrix} 4 & 5 \\ 1 & -2 \end{bmatrix} and C=[3117y]C = \begin{bmatrix} 3 & 11 \\ 7 & y \end{bmatrix}, then x+yx+y is :

Solution

✅ Correct Option: 4

Multiplying, ABAB has first row 4x−1,  5x+24x-1,\;5x+2 and second row 11,  411,\;4.

Transposing puts 4x−14x-1 and 1111 in the first row and 5x+25x+2 and 44 in the second. Comparing with CC: 4x−1=34x-1=3 gives x=1x=1 (consistent with 5x+2=75x+2=7), and y=4y=4.

Hence x+y=5x+y=5.

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