# finding radius/center of circle

• June 4th 2008, 12:31 PM
shawn9356
finding radius/center of circle
find the radius r and the center (h,k) of the following circle
2 2
3 (x-3) + 3y =75
• June 4th 2008, 12:49 PM
Jhevon
Quote:

Originally Posted by shawn9356
find the radius r and the center (h,k) of the following circle
2 2
3 (x-3) + 3y =75

do you mean $3(x - 3)^2 + 3y^2 = 75$?

if so, note that this is: $(x - 3)^2 + y^2 = 5^2$

Now, when a circle is written in the form $(x - h)^2 + (y - k)^2 = r^2$, the center is $(h,k)$ and the radius is $r$. i leave the rest to you
• June 4th 2008, 12:51 PM
Moo
Hi !

Quote:

Originally Posted by shawn9356
find the radius r and the center (h,k) of the following circle
2 2
3 (x-3) + 3y =75

Use ^2 to write exponents :)

You know that the equation of a circle, of center $O(x_O ~,~y_O)$ and of radius R is :

$(x-x_O)^2+(y-y_O)^2=R^2$

Therefore, try to make appear that form.

The reflex will be to divide the whole equation you have by 3, in order to get $(x-3)^2+y^2=\dots$

Then, note that $y=y-0$.
Recognize in your equation $x_O, y_O$ and R :)