need help w/circle

[Shogun]

Find the coordinates of the center and the measure of a radius for the circle whose equation is: (x-8)^2 + (y+4)^2 = 121

I think my answer is:

(H,K) = (8,4) ; r = 11

If I'm wrong or right please let me know. I'm studying for an exam.
I appreciate the help

 

[pka]

A minor sign error: (h,k)=(8,-4).

 

[Shogun]

I don't mean to be a smart alec , but can you please explain how or why it is -4 instead of 4?

 

[Mrspi]

I don't mean to be a smart alec , but can you please explain how or why it is -4 instead of 4?

Well, the equation of a circle with center at (h, k) with radius r is

(x - h)<SUP>2</SUP> + (y - k)<SUP>2</SUP> = r<SUP>2</SUP>

Your equation is

(x - 8)<SUP>2</SUP> + (y + 4)<SUP>2</SUP> = 121

Express each of the binomials as a subtraction, since the general form shows subtractions: ie, (x - h) and (y - k).

(x - (+8))<SUP>2</SUP> + (y - (-4))<SUP>2</SUP> = 11<SUP>2</SUP>

Now, do you see that the center is at (8, -4)?

 

[Shogun]

Yes, I definelty do see it now. Thanks