(cos 3 cos 12- sin 3 sin 12 )^2 + (sin 7 cos 8 + sin 8cos 7)^2
(cos15)^2 + (sin15)^2 = cos^2 15 + sin^2 15 = 1
(cos 3 cos 12- sin 3 sin 12 )^2 + (sin 7 cos 8 + sin 8cos 7)^2
(cos15)^2 + (sin15)^2 = cos^2 15 + sin^2 15 = 1