Tolong bantu kerjakan…….

Kelas 10 Matematika
Bab Trigonometri

2√ab = sin a
(2√ab)² = (sin a)²
4ab = sin² a

(a – b)²
= a² – 2ab + b²
= a² + b² – 2ab
= (a + b)² – 2ab – 2ab
= (a + b)² – 4ab
= (cos a)² – sin² a
= cos² a – sin² a
= cos 2a