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    I got this answer to a vectors question but I tried it a different way and got a different answer and I'm not sure what I've done wrong
    First part of the question is -a+b and that's right
    Next I did OP= OB + 1/4AB
    =b+1/4(-a+b)
    =5/4b - 1/4a
    But when I did it this way OP=OA+3/4AB
    =a+3/4(-a+b)
    =a - 3/4a +3/4b
    =1/4a +3/4b
    and they aren't the same
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    Here's the question
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    (Original post by Purpleunicorn197)
    Here's the question
    Actually never mind- I got it
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    In the first way, you did it wrong. Thats why you got 5/4b - 1/4a. You're meant to subtract the 1/4(AB) because BP runs in the opposite direction to AB, so it should be negative.

    Your second answer is right

    (Edit: Sorry, I only made this post during the time you worked it out so I didn't see you got it, apologies xD)
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    The first method you used, OP = OB + 1/4 AB, you need to use 1/4 BA not AB, because you're going the other way, so instead of using AB = -a+b you need to use BA (which is effectively negative AB), which would be a-b or b + -a

    Hope that helps and good luck today!
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    The second way is correct and the answer should be -1/4a + 3/4b.
    This is because when you did the first way you accidently did OP = OB +1/4AB.
    However if you look at the diagram, you were supposed to do 1/4BA, which is why you ended up with two different values.
 
 
 
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