Coordinate geometry

• donkhead333

  25 Nov 08, 13:54

  

   

  okay, so basically ABCD is a parallelogram even though is doesn't look like one because i did this diagram on paint

  how can i find the coordinates of C?

  Equation of AC: y= - 1/2x + 4

  Equation of BD: y = 4x - 5

  tried using distance formula, but didnt work because there were 2 unknowns..

• Craappiboy

  25 Nov 08, 19:19

  CE=EA

• skythewood

  25 Nov 08, 19:21

  -2, 5

• donkhead333

  25 Nov 08, 20:29

  Originally posted by skythewood:

  -2, 5

  er how did you get that answer? its correct btw.

   

• donkhead333

  25 Nov 08, 20:30

  Originally posted by Craappiboy:

  CE=EA

  er ya...i tried using distance formula...but couldn't get anywhere because there were 2 unknwons involved, the x and y coordinate of C..

• skythewood

  25 Nov 08, 22:05

  can use vector

  AE = EC

• Mikethm

  25 Nov 08, 22:31

  Let C be (h,k)

  Midpoint of AC = [(h+6)/2 , (k+1)/2]

  Midpoint of AC = E (2,3)

  Therefore [(h+6)/2 , (k+1)/2] = (2, 3)

  (h+6)/2 = 2

  h+6 = 4

  h = -2

  (k+1)/2 = 3

  k+1= 6

  k = 5

  Thus C = (-2,5)

  Normally I won't answer if someone gave the correct solution already. Problem is they don't learn vectors in Sec 3.

• chiobabelover

  26 Nov 08, 04:48

  the diagionals will intersect and bisect the diagionals...so the midpoint of A and C is E. That's the proporties of parallelogram.