in the picture you can see the problem, i did a little bit of the way to solve it but i stuck now.
hope you can help
Another way to do it if you can't remember the formulas is through trig substitution. Draw a right triangle such that . Find in terms of x then substitute everything. You'll be left with a nice cancellation and an easy integral. Then back substitute. You'll get the same answer that TheCoffeeMachine is leading you to.