tolong dong kak, nomer 19

π = 180

= cos²30 - sin²150 + 8 cos 135 sin 45
= (√3/2)² - (1/2)² + 8 (-√2/2)(√2/2)
= 3/4 - 1/4 + 8(-2/4)
= 2/4 - 16/4
= -14/4
= -7/2