Question

How do you graph `x^2+y^2+8x-8y-17=0`?

Answer 1

circle: centre=(-4 , 4) , r= 7

Explanation:

The general equation of a circle is:

`x^2 + y^2 + 2gx + 2fy + c = 0`

`x^2 + y^2 + 8x - 8y - 17 = "0 is in this form"`

by comparison: 2g = 8 → g=4 , 2f = -8 → f=-4 and c = -17

centre = (-g , -f ) = (-4 , 4 )

and `r = sqrt(g^2+f^2-c) =sqrt(4^2+(-4)^2+17) =sqrt49 = 7`