Cos 30 = 1/2 √3
sin 135 = sin (180-135)
= sin 45
= 1/2 √2
cos 135 = - cos (180-135)
= - cos 45
= -1/2 √2
cos²30 - sin²135 + 8 sin 45 cos 135 = (1/2 √3)² - (1/2 √2)² + 8. 1/2 √2. (-1/2 √2)
= 3/4 - 1/2 - 4
= - 1 1/4 ----> - 1,25
Cos 30 = 1/2 √3
sin 135 = sin (180-135)
= sin 45
= 1/2 √2
cos 135 = - cos (180-135)
= - cos 45
= -1/2 √2
cos²30 - sin²135 + 8 sin 45 cos 135 = (1/2 √3)² - (1/2 √2)² + 8. 1/2 √2. (-1/2 √2)
= 3/4 - 1/2 - 4
= - 1 1/4 ----> - 1,25