Question

Find the centre and the radius of the circle x2 + y2 + 4x -21 = 0​

Answer 1

Step-by-step explanation:

Given:x2+y2+2x+2y+5=0

⇒x2+2x+1−1+y2+2y+1−1+5=0

⇒(x+1)2+(y+1)2−2−5=0

⇒(x−(−1))2+(y−(−1))2=8

which is comparable with (x−h)2+(y−k)2=r2

Here h=−1,k=−1 and r=22

Hence, the given circle has centre (−1,−1) and its radius=22

Answer 2

Step-by-step explanation:

x2 + y2 + 4x -21 = 0

x2 +y2 + 2 *2*x - 4 - 17 =0

(x-2)^2 + (y-0)^2 = 17

h=2

k= 0

a = √17

center (2,0)

radius √17