Question

Find the center and radius of the circle defined by the equation given below. x ^ 2 + 2x + y ^ 2 + 10y = 15?

Answer 1

Explanation:

Remark

Complete the square for x and for y.

complete for x

x^2 + 2x + (2/2)^2

(x + 1)^2

Complete square for y

y^2 + 10y + (10/2)^2

(y + 5)^2

Now put these two together

(x + 1)^2 + (y + 5)^2 = 15 + (10/2)^2 + (2/2)^2

(x + 1)^2 + (y + 5)^2 = 15 + 25 + 1

(x + 1)^2 + (y + 5)^2 = 41

Answer

Center: (-1,-5)

radius: (sqrt(41) = 6.403