Question

If sin a=-4/5 find cos a​

Answer 1

sin a=-4/5

we have sina=perpendicularp/hypotenuseh=-4/5

let p=-4k

h=5k

by Pythagoras theorem

h²=p²+b²

(5k)²=(-4k)²+b²

25k²-16k²=b²

(3k)²=b²

b=√(3k)²=3k

now

cos a =b/h=3k/5k=3/5