i cant figure out how to simplify these...please help me out..

1. integral (sqrt (x^2-a^2))/x^4 dx

i can get up to integral (a tan^2 x)/(sec^3 x), but i dont know what to do next, because it doesnt easily simplfy...

2. integral (b = 1, a = 0) x(sqrt (x^2 + 4)) dx

3. integral (du)/(u(sqrt(5-u^2)))

4 integral (dt)/(sqrt(t^2 -6t +13))

for this one, i think we are supposed to complete the square and then evaluate the integral..