Let's put these into standard form, first
x^2 + y^2 -2x + 4y + 1 = 0
x^2 - 2x + y^2 + 2x = -1 complete the square on x and y
x^2 - 2x + 1 + y^2 + 2x + 4 = -1 + 1 + 4 factor
(x - 1)^2 + ( y + 2)^2 = 4
This is a circle centered at (1, -2) with a radius of 2
x^2 + y^2 -2x + 4y - 11 = 0
x^2 - 2x + y^2+ 4y = 11
x^2 - 2x + 1 + y^2 + 4y + 4 = 11 + 1 + 4
(x - 1)^2 + (y + 2)^2 = 16
This is a circle with the same center and a radius of 4
The area between the concentric circles =
pi [ 4^2 - 2^2] = pi [16 - 4 ] = 12pi units^2 ≈ 37.7 units^2
