What is the radius of a circle whose equation is x2+y? +8x-6y+21=0?
2 units
3 units
4 units
5 units

  2 units

Step-by-step explanation:

Completing the squares for the x- and y-terms, we get ...

  (x^2 + 8x) +(y^2 -6y) = -21

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

  (x +4)^2 +(y -3)^2 = 2^2

Compare this to the standard form equation for a circle:

  (x -h)^2 +(y -k)^2 = r^2

and we see that the radius (r) is 2.

Step-by-step explanation:

The given equation is

To find the radius of the circle, we have to complete the squares for both variables, that would give us the explicit form, through which we can determine the radius.

So, according to this result the radius is 2, because the explicit expression of a circle states:

Where the right part of the equation is the square power of the radius.

Therefore, the radius is 2 units.