Write the trigonometric expression
cos (arcsin (u))
as an algebraic expression in u

When we use arcsine, we are finding the angle while giving the trigonometric ratio.

Arcsin(u) = theta can be rewritten as:

sin(theta) = u

Sine is opposite over hypotenuse, so u/1 means that the side opposite to theta (the y value) is u, and the hypotenuse is 1.

We can use Pythagorean Theorem to find the adjacent (x value).

1^2 - u^2 = x^2

x = sqrt(1-u^2)

Back to the original question, we are trying to find cos(arcsin(u)). We just solved all the sides for our triangle using arcsin(u). Now we need to do cos(u).

Cosine is adjacent over hypotenuse.

So our answer is sqrt(1-u^2)/1

Or just sqrt(1-u^2)