What is the radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0? units

To answer this, use "completing the square."

x2 + y2 + 8x – 6y + 21 = 0 becomes

x^2 + 8x + 16 - 16 + y^2 - 6y + 9 - 9 + 21 = 0

 (x + 4)^2       -16     + (y - 3)^2     + 12 = 0

or   (x + 4)^2      + (y - 3)^2   = 4

Since 4 = r^2, r = 2 units, and the center is at (-4, 3)

-22

times both sides by 2, times () by 8, add alile terms, move terms, add alike and caculate divide both sides by 3

i am not sure :

step-by-step explanation: