The set of all values of t ∈ R, for which the matrix [e^t, e^-t( sin t-2 cos t), e^-t(-2 sin t- cos t); e^t, e^-t(2 sin t+ cos t), e^-t( sin t-2 cos…

The set of all values of $\displaystyle t \in \mathbb{R}$, for which the matrix $\displaystyle \left[\begin{array}{ccc}e^t & e^{-t}(\sin t-2 \cos t) & e^{-t}(-2 \sin t-\cos t) \\ e^t & e^{-t}(2 \sin t+\cos t) & e^{-t}(\sin t-2 \cos t) \\ e^t & e^{-t} \cos t & e^{-t} \sin t\end{array}\right]$ is invertible, is