Question 1176366
Consider the unit circle, with radius = 1. A point on the unit circle has
coordinates (x,y). Then sin(a) = y/r = y/1 = y, and cos(a) = x/r = x.
From the Pythagorean theorem, we know that x^2 + y^2 = r^2 = 1
If sin(a) = 4/5, we can find cos(a) which is equal to x:
1 - (4/5)^2 = x^2 -> x = sqrt(9/25) = 3/5
cos(a) = 3/5