Vector Proof Question!

  • Thread starter ehjay01
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  • #1
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Hey ive got a vector proof question that i cant get. Sorry i cant provide a diagram but hopefully you can see where i went wrong.

Homework Statement


For triange PQR with with X dividing vector PR in the ratio of 2:3, Y the midpoint of vector PQ and Z the pint of intersection of QX and RY prove that Z divides RY in the ratio 3:1


Homework Equations


first i said that vector RZ was a scalar multiple of vector RY.
RZ=sRY

and my second equation was RZ=tRQ + (1-t)RX

The Attempt at a Solution



first i got both equations in terms of sides of the triange.
RZ=s(RQ+1/2QP),
and RZ=tRQ +(1-t)3/5(RP)
RZ=tRQ+3/5(1-t)(RQ+QP)

then i set the two equations equal to each other and attempted to solve for s and t. I ended up getting s=6/5 and t=2/3. Any help?
 

Answers and Replies

  • #2
Dick
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You can make your job a lot easier by placing one of the vertices at the origin. So say P=0. Now you can take R and Q to be linearly independent and just equate coefficients of R and Q.
 
  • #3
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ok thanks, does it matter which point i use? not only for this question but others like it?
 
  • #4
Dick
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ok thanks, does it matter which point i use? not only for this question but others like it?
No, clearly it can't matter. Try it two different ways if you are having doubts.
 

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