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 = (4-4)/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

(x-k)^2 + (y-h)^2 = r^2

here for center at (0,-2) k=0 and h = -2

x^2 + (y+2)^2 = 25

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