# Math Help - Tough Integral

1. ## Tough Integral

I've tried everything I can think of and I'm not getting it. I'm studying for a final right now, so if there's a trick to doing this question I figure I should know it.

$\int \frac{x + 1}{\sqrt{4x-x^2}} dx$

I've tried trig substitution, integration by parts, normal substitution, etc.

Any ideas?

2. Originally Posted by Thomas
I've tried everything I can think of and I'm not getting it. I'm studying for a final right now, so if there's a trick to doing this question I figure I should know it.

$\int \frac{x + 1}{\sqrt{4x-x^2}} dx$

I've tried trig substitution, integration by parts, normal substitution, etc.

Any ideas?
try this

$\int \frac{x + 1}{\sqrt{4x-x^2}} dx =\int \frac{x-2}{\sqrt{4x-x^2}}dx +\int \frac{3}{\sqrt{4x-x^2}}dx$

$-\frac{1}{2} \int \frac{4-2x}{\sqrt{4x-x^2}}dx+\int \frac{3}{\sqrt{4-(x-2)^2}}dx$

Now make u subs in each integrals

3. Originally Posted by TheEmptySet
try this

$\int \frac{x + 1}{\sqrt{4x-x^2}} dx =\int \frac{x-2}{\sqrt{4x-x^2}}dx +\int \frac{3}{\sqrt{4x-x^2}}dx$

$-\frac{1}{2} \int \frac{4-2x}{\sqrt{4x-x^2}}dx+\int \frac{3}{\sqrt{4-(x-2)^2}}dx$

Now make u subs in each integrals
Yeah...but its not u-substitution for the last one it is $4arcsin\bigg(\frac{x-2}{2}\bigg)+C$

4. Originally Posted by TheEmptySet
try this

$\int \frac{x + 1}{\sqrt{4x-x^2}} dx =\int \frac{x-2}{\sqrt{4x-x^2}}dx +\int \frac{3}{\sqrt{4x-x^2}}dx$

$-\frac{1}{2} \int \frac{4-2x}{\sqrt{4x-x^2}}dx+\int \frac{3}{\sqrt{4-(x-2)^2}}dx$

Now make u subs in each integrals
Also you can make a simpler integral usign a different partial fractions decomposition

5. Originally Posted by Mathstud28
Yeah...but its not u-substitution for the last one it is $4arcsin\bigg(\frac{x-2}{2}\bigg)+C$
It can be 2u=x-2 du=dx

$\frac{3}{\sqrt{4-(x-2)^2}}dx=3\int \frac{1}{\sqrt{4-4u^2}}du=\frac{3}{2}\int\frac{1}{sqrt{1-u^2}}du$

Now sub $u=\sin(\theta), du=\cos(\theta)$

I guess you could do it all in one step with $2\sin(\theta)=x-2$

but I usually do mine one at a time.(We all can't be inte-killer's)

Originally Posted by Mathstud28
Also you can make a simpler integral usign a different partial fractions decomposition
I would like to see the decomp it you can please!

I don't think it can be done.

I thought it only worked with rational functions.

7. Thanks for the help, got the answer. I don't think I've ever used, or seen, that technique before.

But, this was supposed to be an overly hard final to make up for an easy midterm, so no wonder the questions are so hard.