Question

Select the correct answer.
What is the general form of the equation of a circle with its center at (-2, 1) and passing through (-4, 1)?
OA 2+2-4x+2y+1=0
OB. ++4x-2y+1=0
OC. 2+2+4x-2y+9=0
OD. -+2x+y+1=0
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Answer 1

The equation of a circle, with its center (a,b) and radius R is
(x-a)^2 + (y-b)^2 = R^2

For this circle,
(x+2)^2 + (y-1)^2 = R^2

We also know that (-4,1) is a part of the circle, so we replace:
(-4+2)^2 + (1-1)^2 =R^2
4= R^2

The equation of the circle is:
(x+2)^2 + (y-1)^2 = 4
x^2 +4x+4 + y^2 -2x+1 =4
x^2 + 4x + y^2 -2y +1 =0