bentuk (cos135°+cos75°) senilai dngan

Kelas 11 Matematika
Bab Trigonometri Lanjut

cos 135° + cos 75°
= 2 cos ((135° + 75°)/2) cos ((135° - 75°)/2)
= 2 . cos 105° . cos 30°
= 2 . 1/2 √3 . (cos (60° + 45°))
= √3 . (cos 60° . cos 45° - sin 60° sin 45°)
= √3 . (1/2 . 1/2√2 - 1/2 √3 . 1/2 √2)
= (1/4) (√6 - √18)
= (1/4) (√6 - 3√2)