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August 29, 2014

August 29, 2014

Posted by **Anonymous** on Sunday, October 14, 2012 at 11:58am.

D(-18,12)

E(-6,-12)

F(12,6)

Show that the right bisectors of the sides of triangleDEF all intersect at point C(-4,4), the circumcentre of the triangle.

-I found the midpoint of DF then the slope of the midpoint and point E, then found y intercept of new point (midpoint I labelled A) I then subbed point C into the equation of the line found. But it doesn't seem to be equally each other as they should...help!

- Math -
**Reiny**, Sunday, October 14, 2012 at 12:40pmProblem #1 is that you are not finding the right-bisector, but rather the medians

I will describe the steps to find your first right-bisector

1. the midpoint of DF is A(-3, 9)

2. slope of DF = 6/-30 = - 1/5

3. So the slope of the right-bisector of DF is +5

4. equation of right-bisector is

y = 5x + b , but A(-3,9) lies on it, so

9 = 5(-3) + b

b = 24

right-bisector of DF is y = 5x + 24

repeat those steps for one of the other sides

solve those two equations, you should get (-4,4)

Find the equation of the third side, using the above steps

Sub in (-4,4) to see if it satisfies the third equation, it should !!

- Math -
**Anonymous**, Sunday, October 14, 2012 at 1:15pmThanks!!

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