Trig Substitution Verification

I have just worked the following integral and I believe my text has a wrong answer. If anyone would take the time to verify, I would appreciate it.

Initial Problem: $\displaystyle \int\sqrt{4 + 9x^2} dx$

My solution: $\displaystyle \frac{1}{8}[3x\sqrt{4+9x^2} + 4ln|{\sqrt{4+9x^2}+3x}|] + C$

Book solution: $\displaystyle \frac{1}{6}[3x\sqrt{4+9x^2} + 4ln|{\sqrt{4+9x^2}+3x}|] + C$

As you can see, the solutions differ only by the factor's 1/8 and 1/6.

I would appreciate someone verifying for me.