Vectors - Mathswatch ABCD is a parallelogram. The diagonals of ABCD intersect at 0

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skelboi123
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a) Express the vector CA in terms of a
can anybody help please? I have tried CA=2a which was what I think is the correct answer and also as CA=-2a neither are correct?
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ghostwalker
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(Original post by skelboi123)
a) Express the vector CA in terms of a
can anybody help please?
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Note, you're looking for CA, NOT AC.

Going from C to A what are the vectors on the path?
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skelboi123
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(Original post by ghostwalker)
Note, you're looking for CA, NOT AC.

Going from C to A what are the vectors on the path?
Sorry, I've just edited my original post to say that I have tried CA=2a which is what the vectors are but it doesn't mark it as correct either. The screenshot is the other that I tried.
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ghostwalker
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(Original post by skelboi123)
Sorry, I've just edited my original post to say that I have tried CA=2a which is what the vectors are but it doesn't mark it as correct either. The screenshot is the other that I tried.
CA does indeed equal 2a.

The rejection of that must be down to the vageries of Mathswatch. The only think I can think of is that it may insist on having a "+" sign in front of the "2a", but it's not mathematically necessary.
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skelboi123
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Thank you. I will keep trying but I think there must be something wrong with the way Mathswatch is seeing it. a+a, 2a, 2(a),+2a,2 x a. None of which work. So frustrating. I will contact the maths tutor and see if he can sort it out but thank you for your help.
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KAF128___
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(Original post by skelboi123)
Thank you. I will keep trying but I think there must be something wrong with the way Mathswatch is seeing it. a+a, 2a, 2(a),+2a,2 x a. None of which work. So frustrating. I will contact the maths tutor and see if he can sort it out but thank you for your help.
I agree with ghostwalker's answer of 2a. I couldn't find this exact question on MathsWatch but I have found one that is very similar, where the answer I am required to give is 0.5 a + 0.5 b, or 0.5(a+b). When I press the "+" symbol on the right-hand side of the answer box, it pops up with symbols including "half" i.e. "1/2". I submitted my answer as 1/2(a+b) and M/W gave me a tick, eventually... and that was probably a more difficult format of answer to get M/W to accept, so I wouldn't worry about yours ! M/W is known for doing this, quite often ! It's probably something we should run past M/W; I'll check it out with my "superiors" when I return to class in September; they may have a line to M/W to answer such things, or at least a means of obtaining a bit of clarification.
Last edited by KAF128___; 4 weeks ago
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