I need to integrate the following:

7*sqrt(x^2+9)

Here is my work so far:

x=3tan(theta)

d-x=3sec^2(theta)*d-theta

Then:

7*int[sqrt{9tan^2(theta)+9}*3sec^2(theta)*d-theta

Then:

63*int[sec^3(theta)*d-theta]

And I don't know what to do from there. Thank you!