2cos^2 x- tg^2x*(cos2x+1) при cos2x=-1/4

Question

2cos^2 x- tg^2x*(cos2x+1) при cos2x=-1/4

Answer 1

2cos²x- sin²x/cos²x *2cos²x=2cos²x-2sin²x=2cos2x=2*(-1/4)=-1/2=-0,5