Cos48*cos22+cos42*cos68/cos^2 13- sin^2 13

Question

Cos48*cos22+cos42*cos68/cos^2 13- sin^2 13

Answer 1

(cos48*cos22+cos42*cos68)/(cos²13-sin²13)=
=(cos48*cos22+cos(90-48)*cos(90-22))/cos26=(cos48*cos22+sin48*sin22)/cos26=
=cos(48-22)/cos26=cos26/cos26=1