Question

Give the equation of the circle centered at the origin and passing through the point , −90 .

Answer 1

anyway, equation is (x-h)²+(y-k)²=r^2,
(h,k) is center and r is radius since center is (0,0), we get (x-0)²+(y-0)²=r² or simply x²+y²=r² to find r², subsitute the point (-9,0) (-9)²+(0)²=r², 81+0=r², 81=r², 9=r equation is x²+y²=9² or x²+y²=81