The equation of a circle is x2+y2+8x-14y+56=0.

What is the radius of the circle?

r = units

The main formula of a circle is (x-a) ² + (y-b) ² = r², where (a, b) is the center of the circle

x2+y2+8x-14y+56 = x2+8x+y2-14y+56 = (x+4) ²-16 + (y-7) ² - 49 + 56=0

it means (x+4) ² + (y-7) ² - 9=0 and it implies (x+4) ² + (y-7) ²=9

so r²=9, and finally r = 3