Differentiate w.r.t x the expression arccos(x).

Using implicit differentiation, let y equal arccos(x) : y=arccos(x). So x = cos(y), and dx/dy = -sin(y). dy/dx is therefore -1/sin(y). from trig indentities: sin(y) = sqrt(1-cos^2(y)). Substituting gives dy/dx = -1/sqrt(cos^2(y)) which is the derivative of arccos.