Question

Find the center and radius of the sphere x2+2x+y2−4y+z2−8z=60

Answer 1

Hello : 
x²+2x+y²−4y+z²−8z=60
(x²+2x) + (y² - 4y) +(z² - 8z) = 60
(x²+2x+1) -1 +(y² - 4y +4 ) - 4  +( z² - 8z+16) -16 = 60
(x+1)² +(y-2)² +(z - 4)² = 9²
the center is the point : A(-1, 2 , 4)
and radius : 9