Answer
$10~sin^2x-5=-5~cos~2x$
Work Step by Step
$sin^2x+cos^2x=1$
$cos^2x=1-sin^2x$
Use: $cos~2x=cos^2x-sin^2x=1-2~sin^2x$
$10~sin^2x-5=-5(1-2~sin^2x)=-5~cos~2x$
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