Question

Which of the following is the equation of a circle whose center is at the origin and whose radius is 4?

Answer 1

The equation of circle is $(x-a)^{2} +(y-b)^2=r^2$ where (a,b) is the center of circle and r is radius of circle. In your question, (a,b)=(0,0) and r=4 so, the equation is $x^2+y^2=4^2$