1. tentukan nilai dari 8 sin 52,5° cos 7,5° = 2. cos 165° - cos 75° = 3. tentukan nilai cos 2 alpa, jika diketahui cos alpa = 5/13 4. diketahui sudut A dan B su

8 sin 52,5 cos 7,5 = 4 (2 sin 52,5  cos 7,5)
= 4 [ sin (52,5 + 7,5) + sin (52,5 - 7,5)]
= 4 [ sin 60 + sin 45]
= 4 [ 1/2  √3 + 1/2 √2]
= 2√3 + 2√2

cos 165 - cos 75 = - 2 sin 1/2 (165 +75) sin 1/2 (165-75)
= - 2 sin 1/2(240) sin 1/2 (90)
= - 2 sin 120 sin 45
=  - 2 sin (180-60) sin 45
= - 2 sin 60 sin 45
= - 2  (1/2 √3)(1/2 √2)
= - 1/2 √6

cos A = 5/13
cos 2 A = 2 cos² A - 1
cos 2 A = 2 (5/13)² -1 = 2 (25/169 ) - 1 = 50/169 -1 = - 119/169

sin A = 4/5 → cos A = 3/5
cos B = 5/13 → sin B = 12/13
sin (A+B) = sin A cos B + cos A sin B
sin (A+B) = (4/5)(5/13) + (3/5)(12/13) = 20/65 + 36/65 = 56/65