Tentukan nilai bentuk trigonometri cos 67,5 derajat cos 67, 5 derajat

jawab

cos 67,5 cos 67,5 =
= cos² 67,5
=  1/2 ( cos 2x - 1)
= 1/2 (cos 135 - 1)
= 1/2 (-1/2 √2 - 1
= 1/2 (-1/2)(√2 + 2)
= -1/4 (2 + √2)

= 1/2 ( 2 cos 67,5 cos 26,5)