Intgrate(1/sqrt(x^2 + 25))

I started off by letting x=5sinh(a) then substituted in to get

intgral(5cosh(a)/sqrt(25sinh^2(a)+25))

=intgral(cosh(a)/cosh(a))

=x + c

This is not correct, so if anyone could explain where I went wrong and what I should do, that would be very very much appreciated.

Nic