A maths - coordinate geo

• bonkysleuth

  7 Oct 09, 18:51

  Find the equation of the perpendicular bisector of the line segment joining points A(-1,2) and B (7,6)

  I find the gradient of AB and the gradient of the perp. bisector will be -1/AB. Subsequently, i substituted midpoint of AB into the equation. Are my steps correct? The gradient is not the same as AB right?

• TrueHeart

  7 Oct 09, 18:59

  Originally posted by bonkysleuth:

  Find the equation of the perpendicular bisector of the line segment joining points A(-1,2) and B (7,6)

  I find the gradient of AB and the gradient of the perp. bisector will be -1/AB. Subsequently, i substituted midpoint of AB into the equation. Are my steps correct? The gradient is not the same as AB right?

  Hi bonkysleuth,

  your steps are correct.  ( -1/gradient of AB = y-4/x-3 )

• bonkysleuth

  8 Oct 09, 01:15

  thanks. there are some questions in the later part which i still can't resolved. some guiding questions first.

  continued from above

  the perpendicular bisector meets x-axis at D

  find the coordinates of D (5,0), coordinates of C (13,4) such that ABCD is a parallelogram, the area of parallelogram ABCD

  and the question is : the distance from B to CD

• TrueHeart

  8 Oct 09, 06:18

  Originally posted by bonkysleuth:

  thanks. there are some questions in the later part which i still can't resolved. some guiding questions first.

  continued from above

  the perpendicular bisector meets x-axis at D

  find the coordinates of D (5,0), coordinates of C (13,4) such that ABCD is a parallelogram, the area of parallelogram ABCD

  and the question is : the distance from B to CD

  Hi bonkysleuth,

  Just to ask, did the question mention anything else such as shortest distance or longest distance? 

  Cheers

   

• bonkysleuth

  8 Oct 09, 07:30

  Sorry to say, but no the question did not state the shortest dist, etc

• hazelp

  8 Oct 09, 07:56

  distance from B to CD means perpendicular distrance / shortest distance from B to CD.

  Use area of parallelogram = length of CD x distance of B to CD

  you have the value of LHS.  can find length of CD since you already have coordinates of C and D.

• Forbiddensinner

  8 Oct 09, 21:08

  Originally posted by hazelp:

  distance from B to CD means perpendicular distrance / shortest distance from B to CD.

  Use area of parallelogram = length of CD x distance of B to CD

  you have the value of LHS.  can find length of CD since you already have coordinates of C and D.

  Distance from point to a line in general =/= shortest distance

  Maybe bonky will like to ask his teacher if there is anything words missing there?