Find the length of the curve y= (x^2/2) - (ln x / 4) from x = 2 to x = 4.

My attempt:

y' = x- (1/4x)

length = Int 2 - 4 root ( (1 + (x- (1/4x))^2)) dx

= Int 2 - 4 root (1+ x - 1/2 + 1/16x^2) dx

I cant work this out. Is it because I did this part wrong, or just because I can't figure out the integral?