# Math Help - Easy integral problem

1. ## Easy integral problem

How do you find the integral of sqrt[1+81x]? u-substitution and integration by parts does not seem to work.

2. Originally Posted by virtuoso735
How do you find the integral of sqrt[1+81x]? u-substitution and integration by parts does not seem to work.
It should $\int\sqrt{1+81x}\,dx$. Let $u = 1 + 81x$. Your problem reduce to $\frac{1}{81} \int \sqrt{u}\, du$

3. On the contrary, u-sub does work. Try $u = 1+81x$

But for such a trivial integral, it's best to see it as $\frac{1}{81} \int \sqrt{1+81x}~d(1+81x)$ and integrate directly.

Are you sure you did not mean $\sqrt{1+81x^2}$ instead?