# Homework Help: Series sequences

1. Sep 19, 2012

### lovelife

can anyone show me how to do this question ? thanks ...

express (1+x^2)/((1+x)(1+2x)) in partial fraction. (this step i know the solution )
hence,find the constant term in the expansion if (1+x^2)/(-3x(1+x)(1+2x)) in ascending power of x .( then this one dont know ,please help me ) thanks .....

Last edited: Sep 19, 2012
2. Sep 19, 2012

### DonAntonio

$$\frac{1+x^2}{(1+x)(1+2x)}=\frac{1}{2}-\frac{2}{1+x}+\frac{5}{2(1+2x)}=\frac{1}{2}-2(1-x+x^2-x^3+...)+\frac{5}{2}(1-2x+4x^2-8x^3+...)$$

so: what's the constant term of the above? Of course, you could know the answer without doing all the above...can you see how?

DonAntonio

3. Sep 19, 2012

### lovelife

er ... sorry ! i posted the wrong ques ...
actually is ...
hence ,find the constant term in the expansion if
(1+x^2)/(-3x(1+x)(1+2x)) in ascending power of x .

4. Sep 19, 2012

### DonAntonio

Yeah, some mistake, uh?! Really...Well, learn from the already given answer and deduce.

DonAntonio

5. Sep 19, 2012

### lovelife

sorry ! because i type the wrong ques ! could you show me again ! thanks ...

6. Sep 19, 2012

### DonAntonio

No, I won't. It is annoying people is so careless as to malwaste other people's time. Besides this you can use what I already answered!

DonAntonio

7. Sep 19, 2012

### lovelife

ok ! but anyway , thanks for your solution .

8. Sep 19, 2012

### HallsofIvy

Why "anyway"? You have been shown exactly HOW to do it. Apply the same idea to this problem- write as partial fractions, expand each fraction as a geoetric series, and "combine like terms".

9. Sep 19, 2012

### lovelife

because i want the step solution ! because i had do the one solution ,but teacher say the working are wrong !

10. Sep 19, 2012

### Staff: Mentor

NO! That's not the way it works here at Physics Forums. Please read the rules (https://www.physicsforums.com/showthread.php?t=414380), especially the Homework Help Guidelines section. We are happy to help you work the problem, but we won't do your work for you.

Also, homework problems should be posted in the Homework & Coursework section, not in the math technical forums. I am moving this thread to that section.