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Q.If A=[12−35021−11]A = \begin{bmatrix} 1 & 2 & -3 \\ 5 & 0 & 2 \\ 1 & -1 & 1 \end{bmatrix}, B=[3−12425203]B = \begin{bmatrix} 3 & -1 & 2 \\ 4 & 2 & 5 \\ 2 & 0 & 3 \end{bmatrix} and C=[4120321−23]C = \begin{bmatrix} 4 & 1 & 2 \\ 0 & 3 & 2 \\ 1 & -2 & 3 \end{bmatrix}, then compute (A+B)(A+B) and (B−C)(B-C). Also, verify that A+(B−C)=(A+B)−CA + (B - C) = (A + B) - C.

Karnataka PUCKarnataka II PUC Board 2022Subjective· 5mImportance★★★★★
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Matrix addition/subtraction is done entrywise; computing both sides gives the same matrix, verifying A+(B−C)=(A+B)−CA+(B-C)=(A+B)-C.

  1. Compute A+BA+B (add corresponding entries):

A+B=[1+32+(−1)−3+25+40+22+51+2−1+01+3]=[41−19273−14].A+B=\begin{bmatrix}1+3&2+(-1)&-3+2\\5+4&0+2&2+5\\1+2&-1+0&1+3\end{bmatrix}=\begin{bmatrix}4&1&-1\\9&2&7\\3&-1&4\end{bmatrix}.

  1. Compute B−CB-C (subtract corresponding entries):

B−C=[3−4−1−12−24−02−35−22−10−(−2)3−3]=[−1−204−13120].B-C=\begin{bmatrix}3-4&-1-1&2-2\\4-0&2-3&5-2\\2-1&0-(-2)&3-3\end{bmatrix}=\begin{bmatrix}-1&-2&0\\4&-1&3\\1&2&0\end{bmatrix}.

  1. Compute the L.H.S. A+(B−C)A+(B-C) using B−CB-C from step 2:

A+(B−C)=[1+(−1)2+(−2)−3+05+40+(−1)2+31+1−1+21+0]=[00−39−15211].A+(B-C)=\begin{bmatrix}1+(-1)&2+(-2)&-3+0\\5+4&0+(-1)&2+3\\1+1&-1+2&1+0\end{bmatrix}=\begin{bmatrix}0&0&-3\\9&-1&5\\2&1&1\end{bmatrix}.

  1. Compute the R.H.S. (A+B)−C(A+B)-C using A+BA+B from step 1: …

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