The diameter of a circle by definition goes from one "side" of the circle to the other "side" and goes through the center. If we are given the coordinates of the endpoints of the diameter, we need to find the midpoint of that segment to find the center of the circle. The midpoint formula is as follows

. Filling in accordingly, we have

. Doing the math on that gives us a midpoint of (-7, -6), which is also the center of the circle.
Answer:
2.1
Step-by-step explanation:
(21-3)/3 to the power of 2
19/3 to the power of 2
19/9
2.1
The 9 is a coefficient because it is the first one before an 'algebraic number'. :)