Expert: Sherman D. - 6/23/2004

Question
Write the equation for the circle with a center at (-2,3) and radius 4 cm.  

I am not sure how to go about this problem.  

Answer
(x - h)^2 + (y - k)^2 = r^2

where as h = -2 and k = 3, r = 4

(x - (-2))^2 + (y - 3)^2 = (4)^2

(x + 2)^2 + (y - 3)^2 = 16

if you like you can write it like this

((x + 2)(x + 2)) + ((y - 3)(y - 3)) = 16

(x^2 + 2x + 2x + 4) + (y^2 - 3y - 3y + 9) = 16

(x^2 + 4x + 4) + (y^2 - 6y + 9) = 16

x^2 + 4x + 4 + y^2 - 6y + 9 = 16

x^2 + 4x + y^2 - 6y + 13 = 16

x^2 + 4x + y^2 - 6y - 3 = 0

but i would probably just leave it as
(x + 2)^2 + (y - 3)^2 = 16

You should get radius points at

x + 2 = +-4
x = 2 +- 4
x = 6,-2

y - 3 = +-4
y = 3 +-4
y = 7,-1

(6,0), (-2,0), (7,0), and (-1,0)

Info found at http://faculty.ed.umuc.edu/~swalsh/Math%20Articles/circle.html