.
First, sin(x/2)cos(x/2) = .
Second, 1-2sin^2(x/2) = cos(x).
Therefore, sin(x/2)cos(x/2)(1-2sin^2(x/2)) = = . ANSWER
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You need to know basic Trigonometry formulas for multiple arguments (for double arguments, in this case).
See the lesson
- FORMULAS FOR TRIGONOMETRIC FUNCTIONS
in this site.