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Question 1011461:  Find the equation of the angle bisector of the acute angles formed by the lines x+3y=9 and 4x+y=8. 
 Answer by Alan3354(69443)      (Show Source): 
You can  put this solution on YOUR website! Find the equation of the angle bisector of the acute angles formed by the lines x+3y=9 and 4x+y=8. 
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Find the intersection of the 2 lines. 
 x +3y=9 
12x+3y=24 2nd eqn times 3 
----------------- Subtract 
-11x = -15 
x = 15/11 
y = 3 - x/3 = 28/11 
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--> (15/11,28/11) is the intersection 
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Use two lines thru the Origin with the same slopes to find the slope of the bisector. 
x+3y=9 --> m1 = -1/3 
4x+y=8.--> m2 = -4 
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The lines thru the Origin are: 
y = -x/3 and y = -4x 
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The 2 slopes are -1/3 and -4 
The slope is the tangent of the angle with the x-axis. 
atan(-1/3) =~ -18.4349 degs 
atan(-4) =~ -75.9638 degs 
The average =~ -47.1993 degs 
The slope of the bisector = tan(-47.1993) = -1.08 
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Use y-y1 = m*(x-x1) 
y - 28/11 = -1.08*(x - 15/11) 
 
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