Question

What's the standard equation of the circle with the general equation x2 + y2 + 4x – 2y – 20 = 0? answers: 1) (x + 2)2 + (y – 1)2 = 5 2) (x – 2)2 + (y + 1)2 = 25 3) (x + 1)2 + (y – 2)2 = 5 4) (x + 2)2 + (y – 1)2 = 25

Answer 1

Answer:

4).  (x + 2)^2 + (y - 1)^2 = 25.

Step-by-step explanation:

x^2 + y^2 + 4x - 2y - 20 = 0

x^2 + 4x + y^2 - 2y = 20

Completing the square on the x and y terms:

(x + 2)^2  - 4 + (y - 1)^2 - 1 = 20

(x + 2)^2 + (y - 1)^2 = 20 + 4 + 1

(x + 2)^2 + (y - 1)^2 = 25.