Question

25
(3) If Cos A= 3 /5then the value of cos 2A is:​

Answer 1

If Cos A = 3/5 then what will be the value of tan A?

I will answer but firstly it is cos A not Cos A the first letter of a function should never be capitalised.

cos A = 3/5

We know, cos A = base/hypotenuse

Let the base = 3k and hypotenuse = 5k, where k is a positive constant.

By Pythagodras Theorem,

hypotenuse² = base + perpendiclar²

=> (5k)² = (3k)² + p²

=> 25k² = 9k² + p²

=> p² = 25k² - 9k²

=> p² = 16k²

=> p = ±√ (16k²)

=> p = √ (16k²) [accepting only positive value for length]

=> p = 4k

∴ tan A = perpendicular/base

= 4k/3k

= 4/3