Question

proff showed us a trick today for trig substitution:
integral of dx/(x^2/16)
we know: dx/(x^2+1)=arctanx+C

you setup integral as
integral dx/[16*((x^2/16))+1]
=1/16*integral dx/[16*((x/4)^2)+1]
u=x/4
du=dx/4
=
1/4*Integral du/u^2+1
=1/4 arctanx + C

I am having problems using this method for this:
integral of dy/(root225+y^2)
anyone know how??
thanks