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

The radius is 2 units.

Step-by-step explanation:

x^2 + y^2 + 8x − 6y + 21 = 0

Convert this to the general form (x - a)^2 + (y - b)^2 = r^2 by completing the square:

We have:

x^2 + 8x + y^2 - 6y = -21

(x + 4)^2 - 16 + (y - 3)^2 - 9 = -21

(x + 4)^2 + (y - 3)^2 = 4

Comparing with the above general form we see that

r^2 = 4

and therefore r = 2.

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.

the answer is a.

step-by-step explanation:

in three games of golf, alex shot two under par four times.