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    Ans) I used the relationship:
    A . B = |A| |B| cos x

    so 30 = 5 |A| cos ab ---> 1
    And 35= 5 |C| cos bc
    now as |A| = |C|
    it becomes: 35 = 5 |A| cos bc ----> 2

    divide 1 by 2 to get: 30/35 = cos ab /cos bc
    now here is how i imagined those angles to be:

    I then used the trigonometric identities to get:
    6/7 [cos(theta) cos 35 + sin (theta) sin 35] =cos (theta) cos60 + sin (theta) sin 60
    I then rearranged it to get tan and then inverse it and got theta = 61.6 degrees and the answer is 28.4 degrees.

    Where did i go wrong? Any help please will be utterly appreciated
    Thanks a lot
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    I would start by multiplying the two dot product equations to give A · B · B · C = 30 x 35, which simplifies to
    A · C = 1050 / |B|. since you know the angle ac you can work out the modulus of A, which you can then use in the A · B relationship to find a value for angle ab.

    Obviosluy this gives you two possible values for theta, so be careful which one you take as the answer
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