Question

Find an equation of the circle that has center (−1,2) and passes through ( 2,−2) .

Answer 1

Equation of a  circle that has a center at (h,k) and radius of r is
(x-h)²+(y-k)²=r²

so

given center (-1,2)
(x-(-1))²+(y-2)²=r²
(x+1)²+(y-2)²=r²

sub the other point to find r or r²

it passes through (2,-2)
sub 2 for x and -2 for y

(2+1)²+(-2-2)²=r²
(3)²+(-4)²=r²
9+16=r²
25=r²
5=r


the equation is
(x+1)²+(y-2)²=5²