Question

Ques. Derive the formula for cos2A in terms of tangent.

Answer 1

Answer:

Cos2A can be expressed in terms of SinA or CosA as.Cos2A= 2Cos^2A–1. Cos2A= 1–2Sin^2A.Cos2A=Cos^2A-Sin^2A

Answer 2

Step-by-step explanation:

cos 2A = cos^2 A - sin^2 A

cos 2A = cos^2 A - sin^2A/cos^2 A ∙ cos^2 A

⇒ cos 2A = cos^2 A (1 - tan^2 A)

⇒ cos 2A = 1/sec^2 A (1 - tan^2 A)

⇒ cos 2A = 1 - tan^2 A/1 + tan^2 A