tanpa menggunakan kalkulator atau tabel, hitunglah nilai dari: a. cos15°.cos15° b. sin75°+sin15°

Trigonometry.

Calculate without a calculator!
Answer for problem a.
cos² x = 1/2 (1 + cos 2x)
cos 15° cos 15°
= cos² 15°
= 1/2 (1 + cos 30°)
= 1/4 (2 + √3)

Answer for problem b.
sin A + sin B = 2 sin 1/2 (A + B) cos 1/2 (A - B)
sin 75° + sin 15°
= 2 sin 1/2 (75° + 15°) cos 1/2 (75° - 15°)
= 2 sin 45° cos 30°
= 2 (1/2 √2) (1/2 √3)
= 1/2 √6