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C3 Trig Q



My book says I could use either cos(theta+a) or sin(theta-a) for questions like this...

But when I use sin(3theta-a), my values for Rsina=2 and Rcosa=3 are the opposite of what is in the example above... and thus, I'll get different values for tana and eventually 'a'... and my and result is wrong too. What am I doing wrong?

Thanks :smile:
Original post by ps1265A


My book says I could use either cos(theta+a) or sin(theta-a) for questions like this...

But when I use sin(3theta-a), my values for Rsina=2 and Rcosa=3 are the opposite of what is in the example above... and thus, I'll get different values for tana and eventually 'a'... and my and result is wrong too. What am I doing wrong?

Thanks :smile:


Tan(a) will be different
a will be different

Your end result should be the same
Reply 2
Original post by ps1265A


My book says I could use either cos(theta+a) or sin(theta-a) for questions like this...

But when I use sin(3theta-a), my values for Rsina=2 and Rcosa=3 are the opposite of what is in the example above... and thus, I'll get different values for tana and eventually 'a'... and my and result is wrong too. What am I doing wrong?

Thanks :smile:


the alpha would be (90-the alpha) of the previous

what is wrong with final answer .... who knows.
Reply 3
Original post by TenOfThem
Tan(a) will be different
a will be different

Your end result should be the same


Thanks TenOfThem :smile:

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