Question

Find an equation of a circle centred

Answer 1

Center - radius equation for circle of radius r ,centered at (h,k) is :

`(x-h)^(2) + (y-k)^(2) = r^(2)`

you have r = √21

`r^(2) =` (√21)^2 = 21

centre (h,k) = (0,0) so h =0 and k =0

`(x-h)^(2) + (y-k)^(2) = r^(2)`

`(x-0)^(2) + (y -0)^2 = 21`

`x^(2) + y^(2) = 21`