1.

Which among the below matrices has the inverse A^-1=\(\begin{bmatrix}1&-\frac{5}{8}\\0&\frac{1}{8}\end{bmatrix}\)(a) \(\begin{bmatrix}1&5\\0&8\end{bmatrix}\)(b) \(\begin{bmatrix}1&5\\-1&8\end{bmatrix}\)(c) \(\begin{bmatrix}1&5\\0&16\end{bmatrix}\)(d) \(\begin{bmatrix}1&8\\0&8\end{bmatrix}\)I had been asked this question by my school principal while I was bunking the class.My question comes from Invertible Matrices in division Matrices of Mathematics – Class 12

Answer»

Correct ANSWER is (a) \(\begin{BMATRIX}1&5\\0&8\end{bmatrix}\)

Best explanation: CONSIDER the MATRIX A=\(\begin{bmatrix}1&5\\0&8\end{bmatrix}\)

Using the elementary column operations, we write A=AI

\(\begin{bmatrix}1&5\\0&8\end{bmatrix}\)=A\(\begin{bmatrix}1&0\\0&1\end{bmatrix}\)

Applying C2→C2-5C1

\(\begin{bmatrix}1&0\\0&8\end{bmatrix}\)=A\(\begin{bmatrix}1&-5\\0&1\end{bmatrix}\)

Applying C2→C2/8

\(\begin{bmatrix}1&0\\0&1\end{bmatrix}\)=A\(\begin{bmatrix}1&-\frac{5}{8}\\0&\frac{1}{8}\end{bmatrix}\)

A^-1=\(\begin{bmatrix}1&-\frac{5}{8}\\0&\frac{1}{8}\end{bmatrix}\).



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