How to tell how many answers there are? (Trig equations)

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SUMMARY

The discussion focuses on solving trigonometric equations, specifically how to determine the number of solutions within the interval [0, 2π]. When given sec(x) = 2, the corresponding cosine value is cos(x) = 1/2, which yields two solutions. Conversely, for sec(x) = -1, the equivalent cosine equation cos(x) = -1 has only one solution. Utilizing the unit circle is emphasized as a crucial method for visualizing and solving these equations.

PREREQUISITES
  • Understanding of trigonometric functions, specifically secant and cosine.
  • Familiarity with the unit circle and its applications in trigonometry.
  • Basic knowledge of solving equations and identifying valid solutions.
  • Ability to work within specified intervals, particularly [0, 2π].
NEXT STEPS
  • Study the unit circle to identify angles corresponding to specific cosine values.
  • Learn how to convert between secant and cosine functions effectively.
  • Explore the concept of periodicity in trigonometric functions to understand multiple solutions.
  • Practice solving various trigonometric equations within specified intervals.
USEFUL FOR

Students studying trigonometry, educators teaching trigonometric equations, and anyone seeking to improve their problem-solving skills in trigonometric contexts.

Tyrion101
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I'm thinking I may not understand what is a possible solution of a problem and what not. The interval for all of my problems is 0 to 2pi. So I suppose that if my answer was Sec=2, that I'd convert it to Cos, then it would be all of the angles that x = 1/2. I think I have this much right, my confusion is when there are two answers, such as the one listed above, and say sec = -1. What do I do here?
 
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Tyrion101 said:
I'm thinking I may not understand what is a possible solution of a problem and what not.
A solution of an equation is a number that makes the equation a true statement. For example, the equation x2 - 3x + 2 = 0 is true only for x = 1 or x = 2. Any other value of x gives a value on the left side different from zero.
Tyrion101 said:
The interval for all of my problems is 0 to 2pi. So I suppose that if my answer was Sec=2, that I'd convert it to Cos, then it would be all of the angles that x = 1/2.
Yes, that's right.
Tyrion101 said:
I think I have this much right, my confusion is when there are two answers, such as the one listed above, and say sec = -1. What do I do here?
Let's look at the equation sec(x) = 2 first before going off to another problem. Within the interval [0, ##2\pi##], how many numbers are there for which cos(x) = 1/2? Looking at the unit circle is very helpful.

If the equation were sec(x) = -1, then equivalently, cos(x) = -1. For this equation, there is only one solution. Again, the unit circle is helpful.
 
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