help rewriting an integral

hey...so my problem is to rewrite the [integral from 0 to pi/2] of in terms of the elliptic integral E(k, phi) = [integral from 0 to phi] .

please note i am aware elliptic integrals are unsolvable in closed form...i am not looking for a solution, I am just attempting to rewrite the integral to make it look like the form of the elliptic integral E

using the substitution tanu = asinx, I have worked it out to be: [integral from 0 to arctan(asinx)]

but I can't figure out where to go from here. Please help!