Question

Write the equation of the circle whose center is at the origin and whose diameter is 12.

Answer 1

x² + y² = 36 is the answer!

Answer 2

The standard form of the equation of a circle is,
(x - h)² + (y - k)² = r²
where the center is at (h, k) and its radius is r. From the givens above, the equation of the circle is,
x² + y² = (12/2)²
or equal to x² + y² = 36.