Answer:
Step-by-step explanation:
(1). (x - h)² + (y - k)² = r²
where (h, k) are coordinates of a center of the circle with radius r
(2). ( a ± b )² = a² ± 2ab + b²
~~~~~~~~~~~~~~
( 1 , - 2 ) ; r = 3
( x - 1 )² + ( y + 2 )² = 3²
x² - 2x + 1 + y² + 4y + 4 = 9
x² + y² - 2x + 4y - 4 = 0
a = - 2
b = 4
c = - 4
