What is the equation of circle with center at (00) and radius of 7?

##x^2+y^2=49##
The standard form of a circle with a center at ##(hk)## and a radius ##r## is
##(x-h)^2+(y-k)^2=r^2##
Since the center is ##(00)## and the radius is ##7## we know that
##{(h=0)(k=0)(r=7):}##
Thus the equation of the circle is
##(x-0)^2+(y-0)^2=7^2##
This simplifies to be
##x^2+y^2=49##
graph{(x^2+y^2-49)=0 [-16.02 16.03 -8.01 8.01]}