Trig Functions

[deeeelg]

I need to show that h below


can be re written as


where h=height and t=seconds

I am really struggling to get my head around this one. I am aware i need to use the compound identity rules but still cannot get closer to an answer.

any help would be appreciated

 

[mmm4444bot]

Hello. Please show one of your attempts, so that tutors may see what you're trying. Thank you!

Posting Guidelines (Summary)

Welcome to our tutoring boards! :) This page summarizes the main points from our posting guidelines. As our name implies, we provide math help (primarily to students with homework). We do not generally post immediate answers or step-by-step solutions. We don't do your homework. We prefer to...

www.freemathhelp.com

[imath]\;[/imath]

 

[deeeelg]

Hello. Please show one of your attempts, so that tutors may see what you're trying. Thank you!

Posting Guidelines (Summary)

Welcome to our tutoring boards! :) This page summarizes the main points from our posting guidelines. As our name implies, we provide math help (primarily to students with homework). We do not generally post immediate answers or step-by-step solutions. We don't do your homework. We prefer to...

www.freemathhelp.com

[imath]\;[/imath]

I Should have made it clearer sorry. I have not made an attempt. I am stumped as to how i use the compound identity rules for this problem. I have not had any similar problems in my uni tutorials. I am obviously missing a key point but cant put my finger on it.

 

[Dr.Peterson]

I need to show that h below
View attachment 33966

can be re written as
View attachment 33967

where h=height and t=seconds

I am really struggling to get my head around this one. I am aware i need to use the compound identity rules but still cannot get closer to an answer.

any help would be appreciated

It may be helpful if you tell us why you think these should be equal.

In particular, when I graph them, they are not the same (assuming I did it all correctly), so I think there's an error somewhere. Check your copying, among other things.

 

[deeeelg]

It may be helpful if you tell us why you think these should be equal.

In particular, when I graph them, they are not the same (assuming I did it all correctly), so I think there's an error somewhere. Check your copying, among other things.

The question i have been given says "show that h can be re written as". i am aware it is possible as other students in my cohort have completed it i just havent been able to get moving on it

 

[Deleted member 4993]

I need to show that h below
View attachment 33966

can be re written as
View attachment 33967

where h=height and t=seconds

I am really struggling to get my head around this one. I am aware i need to use the compound identity rules but still cannot get closer to an answer.

any help would be appreciated

Google cos(3x) and tell us what you found that can be used for this problem.

show that h below


can be re written as

 

[Steven G]

If in fact the two are equal, then their difference would be 0.
I would also let u=pi*t/5. Then the other angles will be 2u and 3u.
Work with these (cryptic) hints.

 

[Steven G]

Google cos(3x) and tell us what you found that can be used for this problem.

Let's be a bit tougher. Let the student derive the formula for cos(3x) by noting that cos(3x) = cos(2x + x) =.....
There was no google when I had to know what cos(3x) equals.

 

[Dr.Peterson]

The question i have been given says "show that h can be re written as". i am aware it is possible as other students in my cohort have completed it i just havent been able to get moving on it

So, when you said, "I need to show", you were paraphrasing an assignment you were given (and not, for example, trying to reconcile an answer you got with one you were given)?

It will be helpful if you actually show us the whole problem, so we can make sure you aren't misunderstanding something. There may be something in the context that modifies what this means.

Here are the graphs, the first in green, the second in red:

​

And in case I typed something wrong, here are the equations I graphed:

​

Clearly they are not identical. And that means no one can show that they are. Is there anything here that is not what your problem says?

​

You could also check the claim by choosing some value for t, such as t=1, and evaluating both expressions.

 

[Dr.Peterson]

I tried modifying the second equation to see if there might be a typo in the problem, and there is. If I change the second equation to

​

then the graphs are the same. That is, the second form should be

​

I thought the arguments didn't look right!

So tell your teacher the problem is wrong, and then get back to solving it. Do as has been suggested, and use the identities for 3u and 2u, expressing everything in terms of cos(u).

 

[deeeelg]

Dr Peterson, you are correct and that is my fault. i apologize. i typed it incorrectly and your edit is the correct way.

So i took Subhotosh and Stevens advice and have sought out
cos(2x) and cos(3x) and their identities.
i will post my working shortly and see your thoughts.

again i apologize for incorrectly writing the problem. sorry to waste your time