find the equation of a circle passing through the points p(0,-3) and q(4,0) and has its centre on the line x+2y=0

Answer 1

The circle's equation is

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

You know that
(0-h)^2 + (-3-k)^2 = r^2
(4-h)^2 + (0-k)^2 = r^2
h+2k = 0

Now solve for h,k,r

I'd start with

h^2+(k+3)^2 = (h-4)^2+k^2
h = -2k, so

4k^2 + (k+3)^2 = (-2k-4)^2 + k^2
solve that for k, and then you can get h and r.

Answer 2

Thanks a lot steve .... appreciate that !!
But can i use elimination method to solve for h and k ?

Answer 3

sure - do whatever works for you.

Answer 4

Thanks for ur help