Use a right triangle: if sin^(-1)(x) = theta, then sin(theta) = x, so the opposite side is x and hypotenuse is 1, adjacent = sqrt(1-x^2). Therefore: cos(theta) = sqrt(1-x^2), tan(theta) = x/sqrt(1-x^2). This gives: sin^(-1)(x) = cos^(-1)(sqrt(1-x^2)) = tan^(-1)(x/sqrt(1-x^2)) for x >= 0.