Differentiate y = arcsin(x) with respect to x

y = arcsin(x) implies sin(y) = x
Differentiating with respect to x gives: cos(y)*dy/dx = 1So: dy/dx = 1/cos(y)
Noting that cos(y) = sqrt(1 - sin^2(y)): dy/dx = 1/sqrt(1 - sin^2(y)) = 1/sqrt(1 - x^2)