key term - Trigonometric Identity

Definition

A trigonometric identity is an equation involving trigonometric functions that is true for all values of the variables. These identities are fundamental mathematical relationships that hold true regardless of the specific values of the angles involved.

5 Must Know Facts For Your Next Test

1. Trigonometric identities are used to simplify, transform, and evaluate trigonometric expressions.
2. Double-angle, half-angle, and reduction formulas are specific types of trigonometric identities that relate the trigonometric functions of an angle to those of its double or half.
3. Trigonometric identities can be derived from the fundamental relationships between the trigonometric functions, such as the Pythagorean identity.
4. Trigonometric identities are essential in solving trigonometric equations and simplifying complex trigonometric expressions.
5. Applying trigonometric identities correctly is crucial in various fields, including physics, engineering, and mathematics.

Review Questions

• Explain the purpose and importance of trigonometric identities in the context of the topics covered in section 9.3.
  • Trigonometric identities are fundamental mathematical relationships that allow for the simplification, transformation, and evaluation of trigonometric expressions. In the context of section 9.3, which covers double-angle, half-angle, and reduction formulas, these identities are particularly useful. They enable you to express the trigonometric functions of an angle in terms of the functions of its double or half, which is essential for solving trigonometric equations and simplifying complex trigonometric expressions. Mastering these identities is crucial for success in the topics covered in this section.
• Describe how the double-angle, half-angle, and reduction formulas are related to the concept of trigonometric identities.
  • The double-angle, half-angle, and reduction formulas are specific types of trigonometric identities. These formulas express the trigonometric functions of an angle in terms of the functions of its double or half. For example, the double-angle formula for sine states that $\sin(2\theta) = 2\sin(\theta)\cos(\theta)$. This identity allows you to rewrite the sine of a double angle in terms of the sine and cosine of the original angle. Similarly, the half-angle formula for cosine states that $\cos(\theta/2) = \pm\sqrt{(1 + \cos(\theta))/2}$. These identities are essential for simplifying and transforming trigonometric expressions, which is a key skill in the topics covered in section 9.3.
• Evaluate the importance of understanding trigonometric identities in the context of solving problems related to double-angle, half-angle, and reduction formulas. Provide specific examples to illustrate your points.
  • Understanding trigonometric identities is crucial for effectively solving problems involving double-angle, half-angle, and reduction formulas. These identities allow you to rewrite trigonometric expressions in more manageable forms, which is essential for simplifying complex expressions and solving trigonometric equations. For instance, if you are asked to find the value of $\sin(60^{\circ})$, you can use the double-angle formula for sine, $\sin(2\theta) = 2\sin(\theta)\cos(\theta)$, and the fact that $\sin(30^{\circ}) = 1/2$ to derive that $\sin(60^{\circ}) = 2\sin(30^{\circ})\cos(30^{\circ}) = 2(1/2)(\sqrt{3}/2) = \sqrt{3}/2$. Mastering these trigonometric identities allows you to efficiently solve a wide range of problems related to the topics covered in section 9.3.

Related terms

Sine:

The trigonometric function that represents the ratio of the opposite side to the hypotenuse of a right triangle.

Cosine:

The trigonometric function that represents the ratio of the adjacent side to the hypotenuse of a right triangle.

Tangent:

The trigonometric function that represents the ratio of the opposite side to the adjacent side of a right triangle.