Answer
$$\frac{1}{2}\cos e^{-2x}+c.$$
Work Step by Step
Let $ u=e^{-2x}$, then $ du=-2e^{-2x}dx $.
Now, we have
$$\int e^{-2x}\sin e^{-2x}dx =-\frac{1}{2}\int \sin udu
=\frac{1}{2}\cos u+c=\frac{1}{2}\cos e^{-2x}+c.$$
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