How did they get from step a to step b?

  • Thread starter mpatryluk
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In summary, the conversation is about a student struggling with a specific step in solving an integral and questioning a trigonometry relationship. Other students provide tips on how to expand cos(2θ) and suggest using resources like Wikipedia or Wolfram Alpha to find formulas. The conversation ends with the student expressing gratitude for the helpful advice.
  • #1
mpatryluk
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Homework Statement


In my calc book, they're calculating the integral of a specific parametric equation.

Homework Equations


The rest of the question is fine, I am just having trouble with these 2 lines.
attachment.php?attachmentid=59351&d=1370610142.png
I don't understand how cos^2(theta became 1/2(1+ cos2(theta))

Is this a trig relation that I am missing somewhere? If so, they should at least reference it at that step, as opposed to expecting us to memorize and recognize like 50 relationships... Otherwise, I'm lost...

As a side note, I've been looking through trig relations online but can't seem to find any mention of this one, so it makes me feel like I am missing something
 

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  • #2
Hint: Expand cos(2θ).
 
  • #3
D H said:
Hint: Expand cos(2θ).

Considering i don't even know how to begin to start to do that, this tells me i never learned trig properly. I must have really zoned out in quite a few classes when i was in school, lol.

Thank you
 
  • #4
This is really just one of those formulas you either remember or you don't. No one ever tells you all of them and expects you to remember.
Whenever you run into something like this, wikipedia or wolframalpha are your friends. Eg http://www.wolframalpha.com/input/?i=cos(2θ) (look under multiple argument formulas) or http://en.wikipedia.org/wiki/Trig_identities#Double-angle.2C_triple-angle.2C_and_half-angle_formulae .

If you want to calculate it, write cos (or sin) as exponentialfunctions and play around with those.
 
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  • #5
jeppetrost said:
This is really just one of those formulas you either remember or you don't. No one ever tells you all of them and expects you to remember.
Whenever you run into something like this, wikipedia or wolframalpha are your friends. Eg http://www.wolframalpha.com/input/?i=cos(2θ) (look under multiple argument formulas) or http://en.wikipedia.org/wiki/Trig_identities#Double-angle.2C_triple-angle.2C_and_half-angle_formulae .

If you want to calculate it, write cos (or sin) as exponentialfunctions and play around with those.

Ahh that's pretty useful for future reference. Thanks!
 

FAQ: How did they get from step a to step b?

How did they determine the starting point (step a) for their research?

The starting point for any research is often based on previous knowledge or observations that lead to a hypothesis. This could also involve reviewing current literature and identifying gaps in knowledge.

What methods were used to move from step a to step b?

The methods used to move from step a to step b vary depending on the type of research being conducted. Some common methods include experiments, surveys, data analysis, and literature review. The choice of method is based on the research question and the type of data needed.

What challenges did they face in transitioning from step a to step b?

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How long did it take to get from step a to step b?

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What are the implications of the findings in step b?

The implications of the findings in step b depend on the research question and the nature of the research. The findings could have practical applications, contribute to existing knowledge, or raise further questions for future research. It is important for researchers to carefully consider and communicate the implications of their findings.

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