Answer :

[tex]7sin^2x-14sinx+2=-5\\\\7sin^2x-14sinx+2+5=0\\\\7sin^2x-14sinx+7=0\ \ \ \ \ |divide\ both\ sides\ by\ 7\\\\sin^2x-2sinx+1=0\\\\(sinx-1)^2=0\iff sinx-1=0\\\\sinx=1\Rightarrow x=\frac{\pi}{2}+2k\pi=\frac{4k+1}{2}\pi\ (k\in\mathbb{Z})[/tex]

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