Homework Help: Evaluating line integrals

1. Mar 9, 2008

Niles

[SOLVED] Evaluating line integrals

1. The problem statement, all variables and given/known data
I am given a line integral:

$$\int (x^2+y^2)^2ds$$, where C is a circle of radius 3 with centre in (0;0).

Evaluate it.

3. The attempt at a solution
Ok, first I know $$(x^2+y^2)^2$$ = $$81$$. So far, so good.

Then I know for an object in the xy-plane, ds = r*dr*d$$\theta$$. I just insert and use the correct limits, and do the integral?

Thanks in advance.

2. Mar 9, 2008

Niles

No, I am totally wrong.

ds is _not_ what I wrote above, but ds = |r'(t)|dt.

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