Nilai cos² π/6 – sin² 5π/6 + 8 cos 3π/4 sin π/4

Ubah satuan sudut π = 180°
cos² π/6 – sin² 5π/6 + 8 cos 3π/4. sin π/4 =
= (cos 30°)² – (sin 150°)² + 8 cos 135° sin 45°
= (¹/₂√₃)²  -(¹/₂√3)² + 8 (-¹/₂√2)(¹/₂√2)
= (³/₄) -(³/₄) – 8 (¹/₂)
= – 4