$\displaystyle

\int \sqrt{4 x-x^2} dx

$

Okay so I've ran into another bit of a snag...

I know I can solve by the square and ill get

sqrt(4-(x-2)^(2))

but then again the question looks alot like the derivative of arcsin, which can be changed into arcsin...

What would be bestfastestmost efficient way of getting there?