tentukan a sin 70-sin 20 b cos 105+cos 15

Trigonometri.

Jawaban soal a.
sin A - sin B = 2 cos [(A + B) / 2] sin [(A - B) / 2]
sin 70° - sin 20°
= 2 cos [(70° + 20°) / 2] sin [(70° - 20°) / 2]
= 2 (1/2 √2) (0,42)
≈ 0,42 √2

Jawaban soal b.
cos A + cos B = 2 cos [(A + B) / 2] cos [(A - B) / 2]
cos 105° + cos 15°
= 2 cos [(105° + 15°) / 2] cos [(105° - 15°) / 2]
= 2 cos 60° cos 45°
= 2 (1/2) (1/2 √2)
= √2 / 2