Question

Exercitiul asta, va rog, chiar nu stiu cum sa fac​

Answer 1

cos( π/2 +x )=cos( π/2 -(-x) )=sin(-x)=-sin x ;

sin( π/2 +x )=sin( π/2 -(-x) )=cos(-x)=cos x ;

sin x·(-sin x) -cos x·cos x=-sin²x -cos²x =-(sin²x +cos²x)=-1 (unde x∈R).

sin x·cos( π/2 -x) +cos²( π -x)=sin²x +cos²x=1 (unde x∈R).