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# Edexcel P2 watch

1. I have just done it and the only topic that bothers me is the trig idendities. I always seem to have trouble trying to proof such and such.
Is there anything that could help in doing these kind of questions?
2. (Original post by equili3rium)
I have just done it and the only topic that bothers me is the trig idendities. I always seem to have trouble trying to proof such and such.
Is there anything that could help in doing these kind of questions?
well it usually uses sin^2+cos^2=1

get rid of the cosec stuff and change it to 1/cos etc as that might help u get ur head round it

get rid of double angles..u can also work forward from start and backward from end and see if u can join up in middle
3. Always tackle the question from the side with most in it. Always try and express in terms of sin and cos. You will have to apply the sin²X+cos²X=1 identity at some stage. Look out for factorisation or simplification, and other tricks. I really find these proving questions fun and rewarding, have some practise and you will too.

A recent example I did quite easily was: tanX+cotX = 2/sin2X, here goes:
tanX+cotX
= sinX/cosX + cosX/sinX (express in terms of sin and cos)
= sin²X+cos²X/cosXsinX (cross-multiply and add fractions)
= 1/cosXsinX (numerator sin²X+cos²X = 1)
= 2/2cosXsinX (multiply top and bottom by 2, it's an equivalent fraction and gives a 2 on the top as in the right hand side of the identity)
= 2/sin2X (2sinXcosX = sin2X, a double angle identity).

Hope it helps!
4. hi there
5. thanks i guess i will practice in those ways suggested
6. Mainly it just takes practice. When you do lots and lots you start to see the same kind of patterns arising, and generally just get better at it.
Here's me talking like I'm some kind of expert and I'm just doing P2 myself!
7. (Original post by hitchhiker_13)
Mainly it just takes practice. When you do lots and lots you start to see the same kind of patterns arising, and generally just get better at it.
Here's me talking like I'm some kind of expert and I'm just doing P2 myself!
Same here, well I finished P2 this week, but yeah it just takes practise and pretty soon you'll find yourself enjoying the ease and elegance of your proofs. It's so gratifying cracking the puzzles as it were. Think I might beat a B...

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