The equation of a circle which has a center at (-5, 2) can be written as Ax^2 + 2y^2 + Bx + Cy = \(80\). Find the radius of the circle

Guest Apr 15, 2022

#1**-1 **

Best Answer

Since the center is at (-5, 2), The equation of the circle is \((x+5)^2+(y-2)^2=r^2\)

Then you can multiply out \(x^2+10x+25+y^2-4y+4=r^2\)

\(x^2+y^2+10x-4y+29=r^2 \\ 2x^2+2y^2+20x-8y=2r^2-58 \\ 2r^2-58=80 \\ r^2-29=40 \\ r^2=69 \\ r=\sqrt{69} \)

(r has to be positive)

qjin27 Apr 15, 2022