Evaluating Line Integrals for a Circle of Radius 3

[Niles]

[SOLVED] Evaluating line integrals

Homework Statement

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.

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.

 

[Niles]

No, I am totally wrong.

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