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# C3 Trigonometry watch

1. Some proof questions:

1. sin (A+B)/ sin (A-B) = tanA + tanB / (tanA - tanB)

2. sin (A+B) x sin (A-B) = (sinA)^2 - (sinB)^2

I just got (sinA)^2 x (cosB)^2 - (cosA)^2 x (sinB)^2 but I don't know how to get rid of the cosines to just leave sin.
2. 1. LHS expand out and rearrange then convert

2. ???

is it possible to learn the whole c3 in one day

3. well i regret starting doing this...

toodles
4. for Q1, just expand RHS, its much easier
5. (Original post by morebritishthanindian)
1. LHS expand out and rearrange then convert

2. ???

is it possible to learn the whole c3 in one day
no but i managed it with s1
6. (Original post by Pheylan)

well i regret starting doing this...

toodles
?????????????? i've got no idea how you got that
7. (Original post by kai4321)
Some proof questions:

1. sin (A+B)/ sin (A-B) = tanA + tanB / (tanA - tanB)

2. sin (A+B) x sin (A-B) = (sinA)^2 - (sinB)^2

I just got (sinA)^2 x (cosB)^2 - (cosA)^2 x (sinB)^2 but I don't know how to get rid of the cosines to just leave sin.
are these exam style questions???
8. For the second question, remember that sinA^2+cosA^2=1, substitute both cosines and you'll get the answer.

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Updated: January 18, 2010
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