1.

If \(A=\left[ \begin{matrix}{{e}^{t}} & {{e}^{-t}}\text{cos }\!\!~\!\!\text{ }t & {{e}^{-t}}\text{sin }\!\!~\!\!\text{ }t \\{{e}^{t}} & -{{e}^{-t}}\text{cos }\!\!~\!\!\text{ }t-{{e}^{-t}}\text{sin }\!\!~\!\!\text{ }t & -{{e}^{-t}}\text{sin }\!\!~\!\!\text{ }t+{{e}^{-t}}\text{cos }\!\!~\!\!\text{ }t \\{{e}^{t}} & 2{{e}^{-t}}\text{sin }\!\!~\!\!\text{ }t & -2{{e}^{-t}}\text{cos }\!\!~\!\!\text{ }t \\\end{matrix} \right]\) then A is:

A. Invertible for all t ∈ R
B. Invertible only if t = π
C. Not invertible for any t ∈ R
D. Invertible only if \(\text{t}=\frac{\pi }{2}\)
Answer» B. Invertible only if t = π


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