Expert: Richard J. Raridon - 1/22/2005

Question
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Followup To
Question -
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Followup To
Question -
BC and AD are diameters of a circle.  The coordinates are  A(-3, 5)  B(3, 9)  C(1, -1)   What are the coordinates of D?
Answer -
The center of the circle is halfway between B and C so that's (2,4).  That's also halfway between A and D.  Since
A is (-3,5), D is (7,3)



How exaclty did you arrive at your answer?
Answer -
I drew a picture on a piece of graph paper.



So you used the slope to determine where D  was?

Answer
Well, I could have but I didn't need to do so in this case since it was so simple.  You can see that for BC, the x value goes from 1 to 3 and the y value goes from -1 to 9, so the value halfway is (2,4).
That's also the value halfway between A and D.  Since A is
(-3,5) you can see that -3 to 2 is 5 units for x and so add another 5 units to get 7.  For y, it goes from 5 to 4 and therefore the other half goes from 4 to 3.  Got it?