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Problem with a trigonometric equation.

  • #1

Homework Statement


Which of the following is not a possible solution of
0=sinθ+cosθtan^2θ?

A. 3pi/4
B. 7pi/4
C. 2pi
D. 5pi/2


Homework Equations


All trigonometric identities.


The Attempt at a Solution


Too much to write down, at least two pages long, but I've been trying to rewrite the equation so that there's only one trigonometric function left. I would really like a push in the right direction.
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
250
Hi Shawn! :smile:

(have a pi: π and try using the X2 icon just above the Reply box :wink:)
Shawn Garsed said:
… I've been trying to rewrite the equation so that there's only one trigonometric function left. I would really like a push in the right direction.
I'm not sure what you mean by that,

but wouldn't it be easier to factor it, in the form f(θ)g(θ) = 0, so that you can then solve (or in this case, check) the easier equations f(θ) = 0 and g(θ) - 0 separately? :wink:
 
  • #3
I think I got it:

sinθ+cosθtan2θ=sinθ(1+tanθ), therefore θ=0, 180, 135 or 315, which means 5π/2 is not a possible solution.
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
250
I think I got it:

sinθ+cosθtan2θ=sinθ(1+tanθ), therefore θ=0, 180, 135 or 315, which means 5π/2 is not a possible solution.
Perfect! :smile:

(except technically you needed to go above 360°, since 5π/2 > 2π :wink:)
 

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