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

##### 1 Answer

Feb 15, 2016

#### Answer:

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#