Question

Find the center and radius of the sphere whose equation is given by x2+y2+z2−2x−4y+8z+17=0x2+y2+z2−2x−4y+8z+17=0.

Answer 1

We know that
the equation of a sphere is
(x-h)²+(y-k)²+(z-l)²=r²
where (h,k,l) is the center and r is the radius

we have
x²+y²+z²−2x−4y+8z+17=0

Group terms that contain the same variable, and move the constant to the opposite side of the equation

(x²+2x)+(y²-4y)+(z²+8z)=-17
Complete the square. Remember to balance the equation by adding the same constants to each side
(x²+2x+1)+(y²-4y+4)+(z²+8z+16)=-17+1+4+16
(x²+2x+1)+(y²-4y+4)+(z²+8z+16)=4

Rewrite as perfect squares

(x+1)²+(y-2²)+(z+4)²=4

(x+1)²+(y-2²)+(z+4)²=2²

the center is the point (-1,2,-4) and the radius is 2 units