What is the Correct Method to Solve this Trigonometry Problem?

In summary, the conversation discusses the correct method for finding the value of cos(a-b) given the values of sin a, cos b, and the quadrants in which a and b lie. The correct answer is 24/25 and the conversation highlights the importance of taking into account the multiple values of arcsin and arccos.
  • #1
Gurdian
18
0
Not homework just my own revision.

If sin a = –cos b = 3/5 and a and b are both in the second quadrant, what is cos (a – b)?

Now keep getting the answer 0, but the answer is apparently 24/25, now they use the trig subtraction formula, I just did cos ((arcsin(3/5) - arccos(-3/5)) I got 0 as the answer.

Was my method wrong, where did I go wrong with it?
 
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  • #2
Both arcsin and arccos are multivalued. You need to get the possible solutions and see which are in the second quadrant.
 
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  • #3
mathman said:
Both arcsin and arccos are multivalued. You need to get the possible solutions and see which are in the second quadrant.

Ah that's what the explanation was talking about.
 

1. What is trigonometry?

Trigonometry is a branch of mathematics that deals with the study of triangles and the relationships between their sides and angles. It is used to solve problems involving right triangles, circles, and waves.

2. What is the purpose of trigonometry?

The purpose of trigonometry is to calculate unknown angles or sides of a triangle, using known measurements of other angles or sides. It is also used in various applications, such as engineering, physics, and navigation.

3. What are the basic trigonometric functions?

The basic trigonometric functions are sine, cosine, and tangent. These functions are used to relate the angles and sides of a right triangle. Other trigonometric functions such as cotangent, secant, and cosecant are derived from these basic functions.

4. What are the common misconceptions about trigonometry?

One common misconception about trigonometry is that it is only used to solve triangles. In reality, it has many practical applications in fields such as astronomy, architecture, and music. Another misconception is that trigonometry is only used in advanced math courses, when in fact it is taught in many high school math classes.

5. How can I overcome confusion with trigonometry problems?

One way to overcome confusion with trigonometry problems is to practice and review the basic concepts and formulas regularly. It is also helpful to break down a problem into smaller parts and identify which trigonometric function can be used to solve each part. Additionally, seeking help from a teacher or tutor can also clarify any confusion.

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