# Proving Backwards QuestionWatch

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#1
For the 'prove that...' questions in FP2, do you necessarily have to work from left to right? Because I've noticed that it's invariably easier to go backwards. It's just that everything is more obvious, for some reason.
Now, the question, for anyone that might actually know, is whether or not you are penalized for doing this?
And yes, I know you can just write the method backwards afterwards to ensure no marks lost (I have done this not less than twice), but I got bronchitis, ain't nobody got time for that.
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5 years ago
#2
(Original post by Jewagent)
For the 'prove that...' questions in FP2, do you necessarily have to work from left to right? Because I've noticed that it's invariably easier to go backwards. It's just that everything is more obvious, for some reason.
Now, the question, for anyone that might actually know, is whether or not you are penalized for doing this?
And yes, I know you can just write the method backwards afterwards to ensure no marks lost (I have done this not less than twice), but I got bronchitis, ain't nobody got time for that.
Can you give us an example of the sort of question you're talking about?

If A = B then B = A so a proof in either direction is the same thing.

If you're proving an identity, then you can rearrange either side.

However, the statement "A implies B" isn't the same as "B implies A".

Give us an example question and we can be more specific!
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#3
(Original post by davros)
Can you give us an example of the sort of question you're talking about?

If A = B then B = A so a proof in either direction is the same thing.

If you're proving an identity, then you can rearrange either side.

However, the statement "A implies B" isn't the same as "B implies A".

Give us an example question and we can be more specific!
Yeah, that was my reasoning. And actually, it seems the mark scheme for OCR MEI FP2 June 2010 question 4i has answered my question for me, showing the information working from the expression on the right (2coshxsinhx) to become the one on the left (sinh2x).
Mien Fuhrer, I can see!
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