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Q.If A = [[1, 2, -3], [5, 0, 2], [1, -1, 1]], B = [[3, -1, 2], [4, 2, 5], [2, 0, 3]] and C = [[4, 1, 2], [0, 3, 2], [1, -2, 3]] then compute (A + B) and (B - C). Also verify that A + (B - C) = (A + B) - C.

Karnataka PUCKarnataka II PUC Board 2020Subjective· 5mImportance★★★★★
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A+B=[41−19273−14], B−C=[−1−204−13120]A+B=\begin{bmatrix}4&1&-1\\9&2&7\\3&-1&4\end{bmatrix},\ B-C=\begin{bmatrix}-1&-2&0\\4&-1&3\\1&2&0\end{bmatrix}, and A+(B−C)=(A+B)−CA+(B-C)=(A+B)-C.

Concept. Matrix addition/subtraction is performed entrywise (matrices of the same order), and it is associative, which is exactly what the verification illustrates.

Step 1 — A+BA+B:

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}.

Step 2 — B−CB-C:

B−C=[3−4−1−12−24−02−35−22−10+23−3]=[−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}.

Step 3 — A+(B−C)A+(B-C): …

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