Помогите решить (13(sin^2 53-cos^2 53))/cos106

Question

Помогите решить
(13(sin^2 53-cos^2 53))/cos106

Answer 1

Cos^2 x-sin^2x=cos 2x;a sin^2x-cos^2 x=-cos^2 x;
...=13(-cos 2•53)/cos 106=-13cos 106/cos 106=-13;