CosX in terms of Tanx?

  • Thread starter 06Sport
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  • #1
06Sport
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Homework Statement


seems simple, but i am stumped. Says write cos(x) in terms of tan(x).


Homework Equations


would this be a reciprocal equation? or a Pythagorean? I'm lost


The Attempt at a Solution



i don't even know where to begin.
 

Answers and Replies

  • #2
mathwonk
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sin/cos = tan, so cos= sin/tan. har har.

can you use derivatives?
 
  • #3
Moridin
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Write down the two formula for tan x and cos x for a right angle triangle. Are there any similar terms in those equations?

Edit: Beaten to it.
 
  • #4
mathwonk
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DO YOU KNOW WHaT TAN' IS? or 1 + tan^2?
 
  • #5
06Sport
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the angle is unknown. I think that's why its confusing me.

sin/cos = tan, so cos= sin/tan - these are what i have. But would that be the answer? tan= sin/cos ? or cos=sin/tan?
 
  • #6
mathwonk
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i was joking. read my second post.
 
  • #7
06Sport
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:smile: now I am even more confused.

would it be cos=sin/tan?
 
  • #8
arildno
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How can you express sine in terms of cosine?
 
  • #9
06Sport
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How can you express sine in terms of cosine?

i don't know :confused:
 
  • #10
arildno
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Well, what RELATION exists between the sine and cosine of an angle?
 
  • #11
@/@
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[itex]\sin x= \sqrt{1-cos^2x}[/itex]


:devil:
 
Last edited:
  • #12
06Sport
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hmm, sin/cos=tan, cos/sin=cot, sin^2 + cos^2=1

i need cos(theta) in terms of tan(theta) though. Unless that's what we are working up to :)
 
  • #13
arildno
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So, look at the last identity you posted.

What do you get by dividing ôn both sides with cos^{2} ?
 
  • #14
06Sport
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sin^2 = 1/cos^2?
 
  • #16
arildno
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sin^2 = 1/cos^2?

Don't you know how to divide an equation with a number?
 
  • #17
blackcat
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you can express sine in terms of cosine as cos (x-90) where x is in degrees or in radians cos (x-pi/2).
 
  • #18
drpizza
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Am I the first person who thinks it can't be done? Maybe I'm overlooking something, but I'm seeing a sign problem. (+/- when you solve)
 
  • #19
drpizza
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[itex]\sin x= \sqrt{1-cos^2x}[/itex]


:devil:

Only works for 1st and 2nd quadrant angles, that is, angles between 0 and 180 degrees. (or between 0 and 2Pi). Plus, it works for 0 degrees and 180 degrees. If you're in the 3rd or 4th quadrant, then you'd have to use a negative square root.
 
Last edited:
  • #20
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yes,
how to use +- in latex?
 
  • #21
cristo
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how to use +- in latex?

In latex the command for +/- is \pm
 

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