cos 2A in Terms of tan A

We will learn how to express the multiple angle of cos 2A in terms of tan A.

Trigonometric function of cos 2A in terms of tan A is also known as one of the double angle formula.

We know if A is a number or angle then we have,

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

 Multiple Angles

11 and 12 Grade Math

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