Question

№729 помогите срочно ​

Answer 1

16cos4acos2acosasina=8cos4acos2asin2a=4cos4asin4a=2sin8a
(cosa-sina)(cosa+sina(1-cosasina)=cos2a(1-1/2sin2a)
(sin^2a+co^2a)^2-2sin^2acos^2a-1/4cos4a=1-1/2sin^22a-1/4(1-2sin^22a)=3/4
(cos^2a+sin^2a)^2-8cos^2asin^2a=1-2sin^2(2a)=cos4a