Posted by Kate on Wednesday, June 24, 2009 at 1:52am.
The points (4, –5) and (– 4, 1) are endpoints of a diameter of a circle.
(a) Find the center of the circle.
(b) Find the length of the radius of the circle. (Note that this is a distance.) Give the exact answer. Show work.
(c) State the equation of the circle (in standard form). Note that you know the center and the radius from the previous parts.

Math  Damon, Wednesday, June 24, 2009 at 3:55am
average x = (44)/2 = 0
average y = (5 +1)/2 = 2
so center at (0,2)
half the distance between the two given points
d = diameter = sqrt(8^2 + 6^2) =sqrt(64+36) = sqrt(100 = 10
so radius = 5
(xk)^2 + (yh)^2 = r^2
here for center at (0,2) k=0 and h = 2
x^2 + (y+2)^2 = 25