Question 299938
sine = opposite side of right triangle divided by hypotenuse.

cosine = adjacent side of right triangle divided by hypotenuse.

You were given sinx = 3/5, which tells me that the hypotenuse is 5 and the opposite side is 3.

We use the Pythagorean Theorem from geometry to find the adjacent side.

Let A = adjacent side.

(3)^2 + A^2 = 5^2

9 + A^2 = 25

A^2 = 25 - 9

A^2 = 16

Taking the square root of both sides, we get A = 4.

Like I said before, cosine = adjacent side of right triangle divided by hypotenuse.

Then cosx = 4/5

Understood?