# Help with integration

• September 6th 2010, 11:42 AM
ryanali
Help with integration
1) Integral {(x^3)-4x}/{(x^2)+1}^2.what Is The Solution?
2) Integral {x^(1/2)}dx/{1+ X^(1/4)}.what Is The Solution?

thaking you.
• September 6th 2010, 01:01 PM
mr fantastic
Quote:

Originally Posted by ryanali
1) Integral {(x^3)-4x}/{(x^2)+1}^2.what Is The Solution?
2) Integral {x^(1/2)}dx/{1+ X^(1/4)}.what Is The Solution?

thaking you.

1) Use partial fractions.

2) Substitute u = x^1/4.

If you need more help, please show your effort and say where you're stuck.
• September 6th 2010, 01:04 PM
TheCoffeeMachine
1. $\displaystyle \int \frac{x^3-4x}{(x^2+1)^2}\;{dx}$ $\displaystyle = \int \frac{x(x^2-4)}{(x^2+1)^2}\;{dx}$

Let $\displaystyle t = x^2+1 \Rightarrow dx = \frac{1}{2x}\;{dt}$

Then also $x^2-4 = t-5$

We have $\displaystyle \int \frac{x^3-4x}{(x^2+1)^2}\;{dx}$ $\displaystyle = \frac{1}{2}\int \frac{x(t-5)}{xt^2}\;{dt} = \frac{1}{2}\int \left(\frac{1}{t}-\frac{5}{t^2}\right)\;{dt} = \ln{t}+\frac{5}{t}+k$

Hence $\displaystyle \int \frac{x^3-4x}{(x^2+1)^2}\;{dx} = \frac{(x^2+1)\ln(x^2+1)+5}{2(x^2+1)}+k$
• September 7th 2010, 04:22 AM
ryanali
Thank you very much to you both for replying.I tried the first using partial fractions and substitution,but got stuck and the second one i still have no idea how to go forward.
Thank you TheCoffeeMachine.If it is is'nt too much for you could you please help me with the second one too.
• September 7th 2010, 07:25 AM
tom@ballooncalculus
Just in case a picture helps...

In fact, a choice of two - either...

http://www.ballooncalculus.org/draw/intChain/three.png

... or...

http://www.ballooncalculus.org/draw/internal/two.png

... where (key in spoiler) ...

Spoiler:
http://www.ballooncalculus.org/asy/chain.png

... is the chain rule. Straight continuous lines differentiate downwards (integrate up) with respect to the main variable (in this case ), and the straight dashed line similarly but with respect to the dashed balloon expression (the inner function of the composite which is subject to the chain rule).

The general drift is...

http://www.ballooncalculus.org/asy/maps/intChain.png

... or...

http://www.ballooncalculus.org/asy/maps/internal.png

Either way, work anti-clockwise, and find G then F then I.

_________________________________________

Don't integrate - balloontegrate!

Balloon Calculus; standard integrals, derivatives and methods

Balloon Calculus Drawing with LaTeX and Asymptote!
• September 7th 2010, 12:40 PM
mr fantastic
Quote:

Originally Posted by ryanali
Thank you very much to you both for replying.I tried the first using partial fractions and substitution,but got stuck and the second one i still have no idea how to go forward.
Thank you TheCoffeeMachine.If it is is'nt too much for you could you please help me with the second one too.

You should post all the work you have done and then say specifically where you are stuck.