Hey everyone,

So I've been trying for days to find the first positive maximum of the function

(Cos x) * ( sqrt ( 20 sin x ) )

(Ie. highest point on the curve)

I can't even differentiate it, but even if I do figure out the gradient formula and let it equal zero, I don't understand how to solve for x with all those sinea and cosines. I know from looking at the graph that the answer is close to 35, but I need to prove it mathematically. Any help would be greatly appreciated. :)

Ps. I need explanations of how to do it, not just an answer please!

Thankyou!!