Answer
(a) $(-2,-1)$, $5$. (b) see graph. (c) $(-2\pm2\sqrt 6,0)$, $(0,-1\pm\sqrt {21})$
Work Step by Step
(a) Given $x^2+y^2+4x+2y-20=0$, form squares to get $(x+2)^2+(y+1)^2=25$. We can identify its center $(h,k)=(-2,-1)$ and radius $r=5$.
(b) see graph.
(c) To find the x-intercepts, letting $y=0$, we have $x^2+4x-20=0$ which gives $(-2\pm2\sqrt 6,0)$. To find the y-intercepts, letting $x=0$, we have $y^2+2y-20=0$ which gives $(0,-1\pm\sqrt {21})$
