Answer:
Radius=2
Center: (-4,3)
Explanation:
The general equation of a circle is
(x-xo)²+(y-yo)²=r², where (xo,yo) are the coordinates of the center, and r is the radius.
Now: x²+y²+8x−6y+21=0
x²+8x+y²-6y+21=0
(x²+8x+16-16)+(y²-6y+9-9)+21=0
(x²+8x+16)-16+(y²-6y+9)-9+21=0
(x+4)²+(y-3)²-16-9+21=0
(x+4)²+(y-3)²=16+9-21=25-21=4=2²
So
(x+4)²+(y-3)²=2².
Thus, the radius is 2.
The center is at (-4,3)