A line segment is bisected by a line with the equation # 4 y + 3 x = 2 #. If one end of the line segment is at #( 2 , 1 )#, where is the other end?

1 Answer
Jun 14, 2016

One possible other end would be at #color(green)(""(2,-3))#
The equation of all possible answers is #color(green)(2x+4y=-6)#
If the given equation is to be the perpendicular bisector: #color(green)(""(2/25,-39/25))#

Explanation:

#K: 4y+3x=2# (the given bisecting line)

Let #H# be a vertical line through the given end point #(2,1)#.
Since #H# is a vertical line all values of #x in H# are equal to #2#
and #H# intersects #K# at #(2,-1)#
enter image source here
The distance from #(2,1)# to the intersection point #(2,-1)# is #2# units.
Moving another #2# units down #H# would bring us to #(2,-3)#

#K# bisects the line segment from #(2,1)# to #color(green)(""(2,-3))#
i.e. #color(green)(""(2,-3))# is one possible solution value to the given question.

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If we wanted the equation for all solution values
Consider a line #L# drawn through the point #(2,-3)# parallel to #K#
enter image source here
Note the labeling of Line Segment #H# into #AC# and #CD#
which we know from the previous work are in the ratio #1:1#

Consider any other arbitrary Line Segment #J# from #A# at #(2,1)# to the Line #L#.
Note again the labeling that divides #J# into segments #AB# and #BC#

Since #triangle ABC# and #triangle ADE# are similar,
the ratio of #abs(AB):abs(BD)=abs(AC):abs(CE)=1:1#

That is any arbitrary line segment connecting #(2,1)# and line #L# is bisected by #K#

Since #L# has the same slope as #K# and passes through #(2,-3)#
its equation is
#color(white)("XXX")y+3=(-3/4)(x-2)#
or
#color(white)("XXX")3x+4y=-6#

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If we wanted #K# to be a #underline(color(black)("perpendicular"))# bisector of the line segment

Consider the line #M# perpendicular to #K# through #(2,1)#

Since the slope of #K# is #m_K=-3/4#
the slope of #M# must be #m_M=4/3#

and the equation of #M# must be
#color(white)("XXX")(y+3)=4/3(x-2)#
or
#color(white)("XXX")4x-3y=5#
enter image source here

The endpoint of this perpendicular line segment can be derived as the intersection of #M# and #L#

#{(4x-3y=5),(3x+4y=-6):}#

Which gives #(x,y)=(2/25,-39/25)#

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My apologies for the length of this solution.

If anyone can provide a complete solution more briefly, please post it.