# Analytic Geometry

• Jan 27th 2007, 12:13 PM
Universe
Analytic Geometry
Hi,
I have a question, hope you can help.
Triangle DEF has vertices D(-2,4), E(0,-2) and F(6,2). Determine the equation for AB, the right bisector of DF.
I know that the answer supposed to be 4x-y=5.

Thank you very much!
• Jan 27th 2007, 12:53 PM
Universe
I got it :)
I tried again and found the answer.
• Jan 27th 2007, 12:58 PM
ticbol
Quote:

Originally Posted by Universe
I got it :)
I tried again and found the answer.

Heck, I'm late again. I type the slowest.

But since you didn't show your solution, let me post mine, anyway.

If AB is the perpendicular bisector of DF, then the slope of AB is the negative reciprocal of the slope of DF.

If AB is the right bisector of DF, then AB passes through the midpoint of DF.

Slope of DF, m1 = (2-4)/(6 -(-2)) = -2/8 = -1/4
Hence, the slope of AB, m2 = -(-4/1) = 4 -----------***

Midpoint of DF = ((-2+6)/2,(4+2)/2) = (2,3) -------***

Then, the point-slope form of the equation of line AB is
(y-y1) = m(x-x1)
(y -3) = 4(x -2)
y -3 = 4x -8
y = 4x -8 +3