Question

What is the equation of circle whose centre is (0,0) and radius'r' ?​

Answer 1

On the right is a circle with centre (0, 0), radius r and (x, y) any point on the circle. Distance between (0,0) and (x, y) equals the radius, r. If the centre is (0, 0), the equation of the circle will be of the form x2 + y2 = r2.