Given:

And we know,

So

⇒ perpendicular = 3k and base = 4k

By Pythagoras theorem, (hypotenuse)² = (perpendicular)² + (base)²

⇒ (hypotenuse)² = (3k)²+ (4k)² = 9k²+16k² = 25k²

⇒ hypotenuse = 5k

[∵ (hypotenuse)² = 25k²⇒ hypotenuse = √(25k²) = 5k)

Thus, sin A and cos A can be found out.

Multiplying sin A and cos A,

Hence, proved.