cos² π/6 - sin² 3π/4 + 8 sin π/4 cos 3π/4 =... a.-4 1/4 b.-3 3/4 c.4 1/4 d. 4 e.3 3/4 tolong dengan penjelasannya

cos² 30° - sin ² 225° + 8 sin 45 °.cos 225°
= (½√3)² - (-½√2)² + 8.½√2.(-½√2)
= ¾ - ½ - 8.½
= ¾ - ½ - 4
= ¼ - 4
= - 3¾