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# c4 Watch

1. For Q3b.ii., can someone explain to me why 90* is an answer... (I had 45* and 135*)
QP:
http://filestore.aqa.org.uk/subjects...4-QP-JAN13.PDF
MS:
http://filestore.aqa.org.uk/subjects...W-MS-JAN13.PDF
2. (Original post by pippabethan)
For Q3b.ii., can someone explain to me why 90* is an answer... (I had 45* and 135*)
QP:
http://filestore.aqa.org.uk/subjects...4-QP-JAN13.PDF
MS:
http://filestore.aqa.org.uk/subjects...W-MS-JAN13.PDF
When cotx = 0.
3. If you divided the equation by cosx (once you converted sin2x into 2sinxcosx) you shouldn't have.
I'm assuming that's what you did.
4. (Original post by SeanFM)
When cotx = 0.
But tanx=1/0 isn't possible?
5. (Original post by pippabethan)
But tanx=1/0 isn't possible?
If you write cotx in terms of its components, then..
6. (Original post by SeanFM)
If you write cotx in terms of its components, then..
Oh I see, so you write cotx as cosx over sinx
7. (Original post by pippabethan)
Oh I see, so you write cotx as cosx over sinx
Correct.
8. basically yh

cos x
------- - 2sinx = 0
sinx

then u write sin2x in terms of sinx and cosx using double angle formula

then u should be able to solve by factoring, you would get 0 and 90* as shown in the markscheme but you discard 0 as its not in the range

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