Answer
(a) $x^2+y^2=4$
(b) $(x-1)^2+(y-4)^2=1$
Work Step by Step
(a) We can identify the center as $(0,0)$ and radius as $2$, thus the equation is $x^2+y^2=4$
(b) We can identify the center as $(1,4)$ and radius as $1$, thus the equation is $(x-1)^2+(y-4)^2=1$
