How do you graph x^2 + y^2 + 10x - 8y +40 = 0?
1 Answer
Feb 4, 2016
circle : centre = (-5,4 ) and radius = 1
Explanation:
The general equation of a circle is
x^2 + y^2 +2gx+2fy+c = 0 The equation here
x^2+y^2 +10x-8y+40= 0 this equation 'matches' the general equation and by comparison
2g= 10 → g=5 , 2f =- 8 → f = -4 ,c =40 centre = (-g , -f ) = (-5 , 4 )
and
r = sqrt(g^2+f^2-c) = sqrt(5^2+(-4)^2=40) = sqrt(25+16-40 )= 1
