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Homework Help: Finding vector length

  1. Sep 2, 2008 #1
    1. The problem statement, all variables and given/known data


    The question asks to express vector C in terms of A, B, and theta.

    2. Relevant equations

    I would guess the relevant equations to be trig equations.

    3. The attempt at a solution

    I found sin[(180-theta)/2] = k/B (k is a variable I set to equal the right bisected part of C when the angle c was divided in two). Also, sin[(180-theta)/2]= j/A.

    c= 180 - theta. After that however, I don't know how to incorporate theta without using phi. Can you assume that a line stretching from the angle to to make a right angle with vector C bisects the angle into two equal angles? That was how I attempted to solve the problem, but I'm not sure if that works. Any help would be greatly appreciated. Thanks in advance.
  2. jcsd
  3. Sep 2, 2008 #2


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    Homework Helper

    I think you are letting your trigonometry get ahead of your vector addition.

    I would suggest developing equations for the x and y components of A and B that would serve to yield C.

    For simplicity I might suggest letting C lie along the x-axis. Then you know the y-components of the A and B vectors must sum to 0 and the x will sum to C.

    From those equations then look to eliminate any functions of the angle ϕ and leave things in terms of θ.
    Last edited: Sep 2, 2008
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