- #1
Saladsamurai
- 3,020
- 7
I was helping my girlfriend earlier with some HW and now I don't have her text (since she is not here) but I have a question regarding circles.
I did not cover a lot of this material in precalc. and only recall the Standard Form of an equation: x^2+y^2=r^2.
So my question is: if given the equation in General Form, and I wish to know the radius, is the following procedure (completing the square) correct?
Given x^2+y^2+ax+by+c=0
x^2+ax+y^2+by+c=o
x^2+ax+(a/2)^2+y^2+by+(b/2)^2+c=(a/2)^2+(b/2)^2
(x+a/2)^2+(y+b/2)^2=(a/2)^2+(b/2)^2-c
so r=sqrt((a/2)^2+(b/2)^2-c)
is this correct?
thanks,
Casey
I did not cover a lot of this material in precalc. and only recall the Standard Form of an equation: x^2+y^2=r^2.
So my question is: if given the equation in General Form, and I wish to know the radius, is the following procedure (completing the square) correct?
Given x^2+y^2+ax+by+c=0
x^2+ax+y^2+by+c=o
x^2+ax+(a/2)^2+y^2+by+(b/2)^2+c=(a/2)^2+(b/2)^2
(x+a/2)^2+(y+b/2)^2=(a/2)^2+(b/2)^2-c
so r=sqrt((a/2)^2+(b/2)^2-c)
is this correct?
thanks,
Casey