Solving Trigonometric Equations - 0 to 2pi

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SUMMARY

The discussion focuses on solving trigonometric equations within the interval from 0 to 2π. The first equation, sin(θ) = 2/3 with the condition that tan(θ) < 0, requires the application of the identity tan(θ) = sin(θ)/cos(θ) and the double angle formula sin(2θ) = 2sin(θ)cos(θ). The second equation, 2cos²(θ) - cos(θ) = 1, is identified as a quadratic equation in cos(θ), which can be solved using standard algebraic techniques. Participants emphasize the importance of understanding trigonometric identities and quadratic equations for effective problem-solving.

PREREQUISITES
  • Understanding of trigonometric identities, specifically sin(θ), cos(θ), and tan(θ).
  • Familiarity with the double angle formula sin(2θ) = 2sin(θ)cos(θ).
  • Knowledge of solving quadratic equations.
  • Ability to work within specified intervals, particularly 0 to 2π.
NEXT STEPS
  • Study the derivation and applications of trigonometric identities.
  • Learn how to solve quadratic equations in trigonometric contexts.
  • Explore the unit circle and its relevance to trigonometric functions.
  • Practice solving various trigonometric equations using different methods.
USEFUL FOR

Students, educators, and anyone interested in mastering trigonometric equations and identities, particularly in the context of calculus and algebra.

camboguy
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Question 1

sin theta = 2/3 tan theta < 0

sin2 theta = ??


how would i do this?
please help

____
Question 2

solve

2cos^2 theta - cos theta = 1 for 0 <= theta < 2pie


how would i do this one too?
 
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The rules of the forum are that you have to at least try the problem before we can really help. But I can help a little, on the first one square both sides and remember, tan(theta)=sin(theta)/cos(theta) and cos^2(theta)=1-sin^2(theta).
 
Last edited:
For the first question, you ought to know that [tex]tan \theta = \frac{sin\theta}{cos \theta}[/tex] and that [tex]sin2\theta = 2 sin\theta cos\theta[/tex]. The second question is just a quadratic equation.
 

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