Answer:
centre = (- 1, - 2 ) , radius = 5
Step-by-step explanation:
The equation of a circle in standard form is
(x - h)² + (y - k)² = r²
where (h, k) are the coordinates of the centre and r is the radius
Given
x² + 2x + y² + 4y = 20
To obtain equation in standard form use method of completing the square
add ( half the coefficient of the x/y terms )² to both sides
x² + 2(1)x + 1 + y² + 2(2)y + 4 = 20 + 1 + 4
(x + 1)² + (y + 2)² = 25 = 5² ← in standard form
with centre = (- 1, - 2 ) and r = 5
