1.

If A=\(\begin{bmatrix}1&0\\9&4\end{bmatrix}\), then (adj A)A is ______________(a) \(\begin{bmatrix}-4&0\\0&-4\end{bmatrix}\)(b) \(\begin{bmatrix}4&0\\1&4\end{bmatrix}\)(c) \(\begin{bmatrix}4&0\\0&4\end{bmatrix}\)(d) \(\begin{bmatrix}4&0\\0&-4\end{bmatrix}\)I had been asked this question during an interview.This interesting question is from Determinants topic in section Determinants of Mathematics – Class 12

Answer»

Right ANSWER is (C) \(\BEGIN{bmatrix}4&0\\0&4\end{bmatrix}\)

Easy explanation: GIVEN that, A=\(\begin{bmatrix}1&0\\9&4\end{bmatrix}\)

We know that, A(adj A)=(adj A)A=|A|I

∴|A|=4-0=4

⇒A(adj A)=|A|I=\(\begin{bmatrix}4&0\\0&4\end{bmatrix}\).



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