Solving a trigonometric equation

In summary, the given equation is a quadratic in cos(x) and can be factored to find multiple solutions. The solution x=pi can be found by setting cos(x)=-1, and additional solutions can be found by factoring the equation.
  • #1
KiwiKid
38
0

Homework Statement


Solve 2cos(x)^2 + 3cos(x) + 1 = 0 for 0 <= x <= 2pi

Homework Equations


Trigonometric equations, yadda yadda yadda.

The Attempt at a Solution


2cos(x)^2 + 3cos(x) + 1 = 0
cos(x)(2cos(x) + 3) = -1
cos(x) = -1/(2cos(x) + 3)

I then figured out that you get a solution when cos(x) = -1 (so x = pi). However, there are supposed to be multiple solutions, and I don't know how to find these. Any pointers?
 
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  • #2
Notice that the original equation is a quadratic in cos(x).
 
  • #3
SteamKing said:
Notice that the original equation is a quadratic in cos(x).

Ah, found it. I've been messing around with trigonometric identities for half an hour now. Turns out I just had to factor the whole equation. Thanks. =D
 

1. How do you solve a trigonometric equation?

To solve a trigonometric equation, you need to use the properties and identities of trigonometric functions such as sine, cosine, and tangent. You also need to know and understand the unit circle. The steps to solving a trigonometric equation involve simplifying the equation, applying trigonometric identities, and solving for the unknown variable.

2. What are the common strategies for solving trigonometric equations?

There are several common strategies for solving trigonometric equations, including using trigonometric identities, converting to a simpler form using the unit circle, using the quadratic formula, and graphing the equation to find the solutions.

3. How do you use the unit circle to solve trigonometric equations?

The unit circle is a circle with a radius of 1 centered at the origin on a coordinate plane. It is used to represent the values of sine, cosine, and tangent for any angle. To use the unit circle to solve trigonometric equations, you need to understand the relationship between the coordinates on the unit circle and the values of the trigonometric functions. You can then use this knowledge to convert the equation into a simpler form and solve for the unknown variable.

4. What are the key properties and identities used in solving trigonometric equations?

There are several key properties and identities used in solving trigonometric equations, including the Pythagorean identities, the double angle identities, the sum and difference identities, and the reciprocal identities. These properties and identities help simplify the equations and find the solutions.

5. Are there any tips for solving trigonometric equations more efficiently?

Yes, there are a few tips that can help you solve trigonometric equations more efficiently. These include memorizing the common trigonometric identities, understanding the symmetry and periodicity of trigonometric functions, and practicing with different types of trigonometric equations to improve your problem-solving skills.

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