How to solve this identity? Thank you!

Question

$4(sin²a-3/4)=4sin(a+60°)*sin(a-60°)$

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Answer 1 · 2017-12-10T13:01:30

$RHS=4sin(a+60°)*sin(a-60°)$

$=4(sin^2a-sin^2 60°)$

$=4(sin^2a-(sqrt3/2)^2)$

$=4(sin²a-3/4)=LHS$