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# Help with curves and identities and whatnot watch

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1. To be perfectly honest I have no idea what topic this comes under, but anyway here goes:

Show that the curves y = 3sin\theta + 1 and y=2cos2\theta will intersect when

2sin2 + 3sin\theta- 1 = 0

I've spent 20 mins trying to work it out but I have no clue what to do. I haven't seen a question like this before...
2. When do two curves intersect? When they both go through the exact same point.

How do you work out the 1 point that two curves go through?
3. (Original post by claret_n_blue)
When do two curves intersect? When they both go through the exact same point.

How do you work out the 1 point that two curves go through?
uhh....simultaneous equation?
4. (Original post by Alleykat606)
uhh....simultaneous equation?
Yeap
5. (Original post by Alleykat606)
uhh....simultaneous equation?
set them equal to each other

spot that the answer has no cos

Use a well know identity to change your cos to sin
6. (Original post by claret_n_blue)
Yeap
but what does the last equation have to do with it?
7. (Original post by Alleykat606)
but what does the last equation have to do with it?
That's the answer to the question. You are showing the curves intersect at that point. So after your calculations are complete, you should get that answer.
8. (Original post by claret_n_blue)
That's the answer to the question. You are showing the curves intersect at that point. So after your calculations are complete, you should get that answer.
OHHH I get it now. Wording just confused me for a second there. Thanks ever so much!
9. (Original post by Alleykat606)
OHHH I get it now. Wording just confused me for a second there. Thanks ever so much!
No worries

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