The question-

int [(-5x)/(x^2 + 5)^(3/2)] dx

I have-

x=sqrt(5)tan(theta)

dx=sqrt(5)sec^2(theta)dtheta

my solutions manual says that (x^2 + 5) = 5sec^2(theta) <---where does this come from. Is there some trig identity I'm not seeing?

I've attached an image which may show the problem better.