Negative Angle Identities

Trigonometric ratios and functions, the unit circle, inverse trig functions, identities, trig graphs, etc.
eliotmason
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Negative Angle Identities

Postby eliotmason » Tue Oct 29, 2013 6:09 am

So I don't know if I completely understand this Identity. I am working on my homework and this identity is really bothering me and I can't figure it out:

Write the expression in terms of sine and cosine, and simplify so that no quotients appear in the final expression and all expressions are of only.



*So I know that the negative identity for cos is :

- so that will make the top become:



then using the pythagorian identity on top it becomes....



now is where I get lost.... the answer is supposed to be:

*I dont understand how I use the Negative-Angle Identity to make the bottom to be used with the Pythagorean Identities to get to the answer. Thank you in advance for your time and help. :)

buddy
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Re: Negative Angle Identities

Postby buddy » Tue Oct 29, 2013 10:37 am

They've got a list of trig idents here. It shows tan(-@) = -tan(@). Since its squared, you get 1+tan^2(@). This is sec^2(@) which is 1/cos^2(@). That matches what they got.

eliotmason
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Joined: Tue Oct 29, 2013 5:36 am
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Re: Negative Angle Identities

Postby eliotmason » Tue Oct 29, 2013 10:30 pm

buddy wrote:They've got a list of trig idents . It shows tan(-@) = -tan(@). Since its squared, you get 1+tan^2(@). This is sec^2(@) which is 1/cos^2(@). That matches what they got.


That makes perfect sense! Thank you so much for your help! :clap:


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