Need Trigonometry help

  • Thread starter rain.
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Homework Statement


I can't find way to solve [tex]\frac{Sin25 * Sin65}{Cos 40}[/tex]



Homework Equations





The Attempt at a Solution


I looked trough allformulas i have I came up with:
[tex]\frac{Sin25 * Sin65}{Cos 40} = \frac{Sin25 * Cos25}{Cos 40}[/tex]

But then found that formula is:
[tex]Sin 2a =2{Sina * Cosa}[/tex]

Which means what i tried above doesn't work.
 

Answers and Replies

  • #2
rock.freak667
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Try writing sin65 as sin(25+40).
 
  • #3
Mentallic
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Try writing sin65 as sin(25+40).
I don't see how that would help.

But then found that formula is:
[tex]Sin 2a =2{Sina * Cosa}[/tex]

Which means what i tried above doesn't work.

Why not? You gave up on this idea too quickly. Just one extra step and everything will be blatantly obvious.
 
  • #4
rock.freak667
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I don't see how that would help.

I wasn't too sure if it would, I was hoping the cos40 would cancel on expansion.
 
  • #5
Mentallic
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I wasn't too sure if it would, I was hoping the cos40 would cancel on expansion.

Yeah I know where you were coming from :smile: I actually thought it would work too so I quickly scribbled some stuff down but it didn't seem to go anywhere far.
 
  • #6
ehild
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Some more hint: 40=65-25; 90=65+25

ehild
 
  • #7
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thanx.

Is there any goog tuts for learning trigonometry on my own? My textbook is terrible, it starts with hard things soon as explanations part is over. I need something that begins with easier things (but not too easy). I also need good reference for line (Ax+By+C=0) and circle ((x - a) ^2 + (y - b)^2 = r^2).
 
  • #8
vela
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I haven't actually looked through it, but the Schaum's outline for trig is probably a good resource to complement your textbook. Schaum's outlines typically summarize the material and have worked example as well as practice problems with answers.
 
  • #9
Mentallic
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I also need good reference for line (Ax+By+C=0) and circle ((x - a) ^2 + (y - b)^2 = r^2).

Sorry what do you mean by this?
 

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