tolong soal yang nomor 7

cos^2(15) - cos^2(105)
cos^2(15) - (cos(105))^2
cos^2(15) - (-cos(180-75))^2
cos^2(15) - (-cos(75))^2
cos^2(15) - cos^2(75)
cos^2(15) - sin^2(90-75)
cos^2(15) - sin^2(15)
Ingat :
cos(2x) = cos^2(x) - sin^2(x)
cos(2.15) = cos 30 = 1/2 √3