Write the trigonometric expression as an algebraic expression in u. cos (sin-1 u)

Cos(arcsin(u)) = √(1 - u²)


You want cos(α) where sin(α) = u.
You know that
  cos(α)² + sin(α)² = 1
  cos(α)² = 1 - sin(α)² = 1 - u²
  cos(α) = √(1 - u²)

Cbottom left is the correct one.

Iknow one of the answers is a and maybe b but not 100% sure about b