Question

(Cos2a-sin2a)^2-sin8a/2cos4a

Answer 1

$<var>sin^22a-2sin2acos2a+cos^22a-\frac{2sin4acos4a}{2cos4a}=</var>$ 

$<var>1-sin4a-sin4a=1-2sin4a=</var>$