# Parametric Equation Question

1. Jul 23, 2011

### waealu

For an assignment, I am supposed to find the parametric equation for the circle:
x^2+y^2=a^2,
using as a parameter the arc length, s, measured counterclockwise from the point (a,0) to the point (x,y).

I understand that the parametric equation for a circle is x=a*cos(t) and y=a*sin(t), but I'm not sure what they are asking me to do in this problem.

Would anyone be able to get me started on this problem?

Thanks

2. Jul 23, 2011

### SammyS

Staff Emeritus
How is t (in radians?) related to the arc length, s?

3. Jul 23, 2011

### waealu

Nevermind, I was able to figure it out. They are looking for x=a*cos($\Theta$)=a*cos(s/a) and y=a*sin($\Theta$)=a*sin(s/a).

Thanks, though.

4. Jul 23, 2011

### SammyS

Staff Emeritus
Yes.

You're welcome.