Question

formula of cos4a to find its value​

Answer 1

Answer:

cos 4A = cos (2 ∙ 2A) = 2 cos2 (2A) - 1

⇒ cos 4A = 2(2 cos 2A - 1)2 - 1

⇒ cos 4A = 2(4 cos4 A - 4 cos2 A + 1) - 1

⇒ cos 4A = 8 cos4 A – 8 cos2 A + 1