1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help on triangle proof question

  1. Dec 17, 2005 #1
    Hello,
    Here is the question:
    [​IMG]
    Here are 2 different ways i tried to approach the question:
    In the first way, i tried using pythagoreom theorem by making a right angle, but after i did the question i realized since it did not say it was a right triangle, ic annot assume there is a 90 degrees angle and i cannot use the pythagoras theorem.
    [​IMG]
    Second way i tried using vector addition. However you can see at the end i was stuck.
    [​IMG]
    though i believe vector addition is the way to solve this problem, however we had never done any problems involving the squared of a vector unless it was using the pythagoras theorem,
    any suggestions in what i did wrong or what i could do?

    Sorry for my messy writing hehe.

    thanks
    byron
     
  2. jcsd
  3. Dec 17, 2005 #2

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    Byron,

    Try this. Drop a perpendicular from A to the line segment BC. Call its length h and the distance between the intersection point and the midpoint x. Now you can use Pythagoras to solve for x and h from which you can calculate AD.
     
  4. Dec 17, 2005 #3

    Hurkyl

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I know why you can't do it with vector addition: nowhere in your work did you make use of the fact that D is the midpoint of the line segment BC.

    (In fact, you didn't even made use of the fact that D is on the line through B and C!)
     
  5. Dec 17, 2005 #4
    didnt i do it in the first try? but if you drop a perpendicular from A to line segment BC then how would u prove that it is a right angle? but i think i did that in first try..

    though i am going to try coordinate proofs right now :D i think that is the solution
     
  6. Dec 17, 2005 #5

    Hurkyl

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I only looked at your vector addition approach. I agree that ought to be the easiest solution. (unless you're particularly adept with synthetic geometry)
     
  7. Dec 17, 2005 #6
    i got the answer by using coordinate proofs and making LS = RS

    thanks for all your help :D
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Help on triangle proof question
  1. Triangle proof help (Replies: 14)

Loading...