03 Dec, 11:14AM in sunny Singapore!
Home → Homework Forum →

coodinate geometry ( immediate help needed!)

Subscribe to coodinate geometry ( immediate help needed!) 5 posts

Please Login or Signup to reply.
  • bonkysleuth
    bonkysleuth's Avatar
    314 posts since Mar '07
    • 04 Aug `08, 4:49PM

      in a rectangle ABCD, the coordinates of A and B are (4,2) and (2,8) respectively. given that the equation of AC is y = x - 2, find

       

      (a)the equation of BC.

       

       

  • Moderator
    eagle
    eagle's Avatar
    17,972 posts since Aug '01
    • 04 Aug `08, 4:56PM

      Because it is a rectangle ABCD, it should be clear that the line BC is perpendicular to the line AB

      Gradient of AB = (8-2)/(2-4) = -3

      Hence gradient of BC = 1/3

      Thus, using coordinate of point B,
      y - 8 = 1/3 (x - 2)

      Equation of BC: y = 1/3 x + 22/3

       

      Eagle
      Owner of Strategic Tuition

  • bonkysleuth
    bonkysleuth's Avatar
    314 posts since Mar '07
  • bonkysleuth
    bonkysleuth's Avatar
    314 posts since Mar '07
    • 04 Aug `08, 5:30PM

      okay, suppose the question now wants me to find coordinates of D. can I use the fact that since the figure is a rectangle, the number of units for each opposite site is equal? Firstly, you get the coordinates of C. then you find coordinates of D by counting the number of units on the opposite site.

       

      Is this method acceptable? or is there a way to find it? i got the answer. it's (16,6) and its correct. just wanna check whether there is any alternative to solve this question.

  • Moderator
    eagle
    eagle's Avatar
    17,972 posts since Aug '01
    • 04 Aug `08, 9:43PM

      Can, but wouldn't that be a bit too troublesome?

      Another method is to make use of the property of a parallelogram. Midpoint of AC = midpoint of BD.

      That would be a much faster and neater way of solving.

       

      Eagle
      Owner of Strategic Tuition

       

Please Login or Signup to reply.