Chapter 14 - Sequences, Series, and the Binomial Theorem - 14.2 Arithmetic Sequences and Series - 14.2 Exercise Set - Page 903: 56

$(x+2)^2+(y-1)^2=20$

The standard equation of the circle is $(x-x_0)^2+(y-y_0)^2=R^2,$ where $(x_0,y_0)$ is centre coordinate and $R$ - radius. In our case $x_0=-2, y_0=1$ and $R=2\sqrt5$. Hence the circle's equation is: $(x-(-2))^2+(y-1)^2=(2\sqrt5)^2$ $(x+2)^2+(y-1)^2=20$