Find Radian Angle: Value of cos θ = -1/2, π ≤ θ ≤ 2π

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SUMMARY

The discussion focuses on finding the radian angle θ for the equation cos θ = -1/2 within the interval π ≤ θ ≤ 2π. The first solution identified is θ = 2π/3, which corresponds to the second quadrant. The second angle, located in the third quadrant, can be determined by adding π to the reference angle of 2π/3, resulting in θ = 4π/3. This method effectively utilizes the properties of the unit circle and the cosine function.

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  • Understanding of trigonometric functions, specifically cosine.
  • Familiarity with the unit circle and its quadrants.
  • Knowledge of radian measure and angle conversion.
  • Basic geometry skills for visualizing angles and their properties.
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  • Study the unit circle to visualize angles and their corresponding cosine values.
  • Learn about the properties of trigonometric functions in different quadrants.
  • Explore the concept of reference angles and their applications in trigonometry.
  • Practice solving trigonometric equations involving cosine for various intervals.
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Students studying trigonometry, educators teaching angle measurement, and anyone seeking to deepen their understanding of the cosine function and its applications in different quadrants.

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Homework Statement


For the value of cos θ, determine the radian value of θ if π ≤ θ ≤ 2π.

Value is -1/2.

Homework Equations

The Attempt at a Solution


I got the first value which is cos-1(-1/2) which I got (2π)/3.
However I am unsure how to get the second value.
I thought that since the first value is in second quadrant the other value is in the third quadrant, then I would take θ-π to find my value in the quadrant. But my answer was incorrect. Can someone pls guide me? Thx.
 
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Veronica_Oles said:

Homework Statement


For the value of cos θ, determine the radian value of θ if π ≤ θ ≤ 2π.

Value is -1/2.

Homework Equations

The Attempt at a Solution


I got the first value which is cos-1(-1/2) which I got (2π)/3.
However I am unsure how to get the second value.
I thought that since the first value is in second quadrant the other value is in the third quadrant, then I would take θ-π to find my value in the quadrant. But my answer was incorrect. Can someone pls guide me? Thx.
What angle in the 3rd quadrant has a cosine of -1/2? Draw a unit circle and use basic geometry to find that angle.
 
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