# Integrate (1+x+x^2) / x(1+x^2) for x. Partial dractions?

1. Jan 21, 2006

### teng125

integre (1+x+x^2) / x(1+x^2)
pls help....
i used partial fraction and obtain the answer of ln x - 1/2 ln (1-x^2) + arctan x
is it correct??

2. Jan 21, 2006

### HallsofIvy

Staff Emeritus
That's not what I get. HOW did you get that? What was the partial fractions expansion?

3. Jan 21, 2006

### teng125

i got 1 +x +x^2 = A(1+x^2) + B(x^2) + Cx
then let x =1 and -1 and again x=0

is it correct??

4. Jan 21, 2006

### VietDao29

Looks good. So what are your A, B, and C?
Remember that:
$$\frac{1 + x + x ^ 2}{x(1 + x ^ 2)} = \frac{A}{x} + \frac{Bx + C}{1 + x ^ 2}$$
What does your final result look like?

5. Jan 21, 2006

### teng125

A=1 B=0 and C=1

6. Jan 21, 2006

### teng125

is it right

7. Jan 21, 2006

### VietDao29

Yup, it looks good. So:
$$\int \frac{1 + x + x ^ 2}{x(1 + x ^ 2)} dx = \int \left( \frac{1}{x} + \frac{1}{1 + x ^ 2} \right) dx = ?$$
Can you integrate this? And what's your answer, then?

8. Jan 21, 2006

### teng125

oh.....i intgre wrongly on the above....is should be ln x + arctan x rite??

9. Jan 21, 2006

### VietDao29

Looks about right, but don't forget the constant of integration.

10. Jan 21, 2006

### Ouabache

Are they teaching integration in precalculus now?

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