(Solved) Equivalent Trig Expressions

marinejas

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3 years ago

1. Write an expression that it equivalent to each of the following expressions using cofunction identities.
a) cos pi/16 b) tan 9pi/10

2. Write an expression that is equivalent to each of the following expressions, using the related acute angle.
a) cos 2pi/3 b) sin 5pi/4 c) tan 11pi/6

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bio_man

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marinejas Author

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3 years ago Edited: 3 years ago, marinejas

Hi! thanks and yes I needed it, also not sure if you saw my reply from my last post but just wanted to clarify a few things about finding the possible equations from the graph. Slight Smile

Post Merge: 3 years ago

I also have another part to this question (part B) where you have to fill in a chart, can I still post it here or should I post it separately?

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bio_man

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3 years ago

Post it here

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marinejas Author

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3 years ago

alright thanks

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bio_man

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3 years ago

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marinejas Author

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3 years ago

for 1. a) Just to confirm, you used the cofunction identity, sin theta = cos(pi/2 - theta), and also by using my calculator I can go from the 2nd step to to 7/16pi, is it important to add all the steps? On a test would I lose marks?

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bio_man

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3 years ago

Yeah, you don't need to show all those steps, I just do it for you 😄

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marinejas Author

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3 years ago

Ok thanks for that then Slight Smile

also for 1. b) can I write it as tan (-2/5pi) = cot 9pi/10 ?

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bio_man

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3 years ago

No, they're completely different

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marinejas Author

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#10

3 years ago Edited: 3 years ago, marinejas

Ok just wanted to make sure, and sorry if I keep asking the same question but for 2 I got everything correct except the part on whether you have to add pi or not, for a) why did you add pi to the pi/3, as well as for b why use 2pi.. etc

Post Merge: 3 years ago

Oh wait nvm I think I git it now, whether I add or subtract from 2nd or 3rd quad (from photo) I still get the answer, but I just answers of for example 2. a) cos(2/3pi), cos(-2/3pi), and cos(4/3pi) I still end up getting the answer of -1/2. Sorry if that didn't make much sense, hope you get what I mean.

Post Merge: 3 years ago

Can you confirm if this is correct or not?

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bio_man

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#11

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3 years ago

Okay, so if you know the acute reference angle θ, and you want to find the actual angle in quadrant 2, you do:

π - θ

In third quadrant:

θ + π

In fourth:

2π - θ

Does that answer your question?

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marinejas Author

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#12

3 years ago

I think I figured it out now, if you see what I wrote above including the picture I use.
Overall, would you say I'm correct about that?

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bio_man

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#13

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3 years ago

All that is true if you want to find the acute reference angle, but if you know the acute reference angle and want to find the actual angle, you do what I wrote above.

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