Answer
a) $x^2+y^2=4^2 ; z=0$
b) $y^2+z^2=4; x=0$
c) $x^2+z^2=4; y=0$
Work Step by Step
Definition: The equations of a circle having radius $r$ with center at origin and lying in the xy-plane, yz-plane and xz-plane are represented as:
$x^2+y^2=r^2$ when z=0 , $y^2+z^2=r^2$ when x=0 and $x^2+z^2=r^2$ when y=0
Thus, we have:
a) $x^2+y^2=4^2 ; z=0$
b) $y^2+z^2=4; x=0$
c) $x^2+z^2=4; y=0$
