Question

докажите что cos 75 + cos 45 - cos 15 = 0

Answer 1

cos 45 = cos 15 - cos 75

cos 45 = 2sin ((15+75)/2)*sin((75-15)/2)

cos 45 = 2sin 45*sin 30

√2/2 = 2 * √2/2 * 1/2

√2/2 = √2/2