A line segment is bisected by a line with the equation - 2 y - 5 x = 2 . If one end of the line segment is at ( 8 , 7 ), where is the other end?

1 Answer
Mar 26, 2017

(-328/29, -21/29) ~~(-11.31, -.724)

Explanation:

  1. Put the line in y-intercept form y = mx + b:
    -2y = 5x + 2
    y = -5/2x -1
    m = -5/2
    The perpendicular bisector slope = -1/m = 2/5

  2. Find the equation for perpendicular bisector the line with (8,7):
    y = 2/5x + b
    7 = 2/5*(8/1) + b
    7 = 16/5 + b
    35/5 - 16/5 = 19/5
    y = 2/5x + 19/5

  3. Find the midpoint (intersection point) of the two lines
    -5/2x -1 = 2/5x + 19/5
    -5/2x - 2/5x = 19/5 + 1
    -25/10x - 4/10 x = 19/5 + 5/5
    -29/10x = 24/5
    x = 24/5 * -10/29 = 24/1 * -2/29 = -48/29
    #y = -5/2 * -48/29

y = (-5/1 * -24/29) - 29/29
y = 120/29 - 29/29 = 91/29
midpoint point (-48/29, 91/29) ~~(-1.655, 3.138)

enter image source here

  1. Length from midpoint to (8,7), 1/2 length of line segment:
    sqrt((7 - 91/29)^2 + (8 --48/29)^2) = sqrt ((203/29 - 91/29)^2 + (232/29 + 48/29)^2) = sqrt((112/29)^2 + (280/29)^2) = sqrt((112^2+280^2)/(29^2) ) = sqrt(3136/29) = 56/sqrt(29) = (56sqrt(29))/29~~ 10.4

  2. Length of the line segment:
    2 * 56/sqrt(29) = 112/sqrt(29) = (112sqrt(29))/29 ~~ 20.8

  3. Use proportions to find the endpoint:
    x/(280/29) = (112/sqrt(29))/(56/sqrt(29)); " "x = 560/29

y/(112/29) = (112/sqrt(29))/(56/sqrt(29)); " " y = 224/29

enter image source here

Endpoint (8 -x, 7 - y):
(8-560/29, 7-224/29) = (-328/29, -21/29) ~~(-11.31, -.724)

CHECK using the line equation & finding length:

-21/29 = 2/5 * -328/29 + 19/5

-21/29 = -656/145 + 551/145#

-21/29 = -105/145 = -21/29

Length of 1/2 line from (-328/29, -21/29) to midpoint (-48/29, 91/29):

sqrt((91/29 - -21/29)^2 + (-48/29 --328/29)^2) = sqrt((112/29)^2 + (280/29)^2) = sqrt(90944/29^2) = sqrt(3136/29) = 56/sqrt(29)