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# C3 proof question watch

1. Hi

I was going through a C3 paper (OCR MEI, June 2009) and came across this question attached below.

Please could somebody explain part (ii)? I proved the first part correctly, but I have no idea how to then go on to prove the second part… the mark scheme says that I have to prove the first parts to be positive? I still don't get it ahhh

Would really appreciate if anybody could help! Thanks
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2. (Original post by Babs Posh)
Hi

I was going through a C3 paper (OCR MEI, June 2009) and came across this question attached below.

Please could somebody explain part (ii)? I proved the first part correctly, but I have no idea how to then go on to prove the second part… the mark scheme says that I have to prove the first parts to be positive? I still don't get it ahhh

Would really appreciate if anybody could help! Thanks

So you need to prove that

To do this you'll need to prove that both brackets are . Think about how you can use (B) for this. Please post your thoughts/working if you get stuck.
3. (Original post by Babs Posh)
Hi

I was going through a C3 paper (OCR MEI, June 2009) and came across this question attached below.

Please could somebody explain part (ii)? I proved the first part correctly, but I have no idea how to then go on to prove the second part… the mark scheme says that I have to prove the first parts to be positive? I still don't get it ahhh

Would really appreciate if anybody could help! Thanks
look at the second bracket in (A), , can you think of any way to show this is always positive, possibly with a substitution?

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