Definitions of Cosecant and Cotangent

Oct 13, 2025 by windailys.com 124 views

Introduction

In trigonometry, we often encounter expressions involving trigonometric functions such as sine, cosine, and their reciprocals. One of the fundamental identities in trigonometry is the Pythagorean identity, which states that $\sin^2 \theta + \cos^2 \theta = 1$ . However, in this problem, we are given an expression involving cosecant and cotangent functions, and we need to simplify it.

The Expression

The given expression is $\csc^2 \theta + \cot^2 \theta - 1$ . To simplify this expression, we need to use the definitions of cosecant and cotangent functions.

Definitions of Cosecant and Cotangent

The cosecant function is defined as the reciprocal of the sine function, i.e., $\csc \theta = \frac{1}{\sin \theta}$ . Similarly, the cotangent function is defined as the reciprocal of the tangent function, i.e., $\cot \theta = \frac{1}{\tan \theta} = \frac{\cos \theta}{\sin \theta}$ .

Simplifying the Expression

Using the definitions of cosecant and cotangent functions, we can rewrite the given expression as follows:

$\csc^2 \theta + \cot^2 \theta - 1 = \left(\frac{1}{\sin \theta}\right)^2 + \left(\frac{\cos \theta}{\sin \theta}\right)^2 - 1$

Applying the Pythagorean Identity

We can simplify the expression further by applying the Pythagorean identity, which states that $\sin^2 \theta + \cos^2 \theta = 1$ . We can rewrite the expression as follows:

$\left(\frac{1}{\sin \theta}\right)^2 + \left(\frac{\cos \theta}{\sin \theta}\right)^2 - 1 = \frac{1}{\sin^2 \theta} + \frac{\cos^2 \theta}{\sin^2 \theta} - 1$

Simplifying the Expression

We can simplify the expression further by combining the fractions:

$\frac{1}{\sin^2 \theta} + \frac{\cos^2 \theta}{\sin^2 \theta} - 1 = \frac{1 + \cos^2 \theta}{\sin^2 \theta} - 1$

Applying the Pythagorean Identity Again

We can simplify the expression further by applying the Pythagorean identity again:

$\frac{1 + \cos^2 \theta}{\sin^2 \theta} - 1 = \frac{1 + \cos^2 \theta}{\sin^2 \theta} - \frac{\sin^2 \theta}{\sin^2 \theta}$

Simplifying the Expression

We can simplify the expression further by combining the fractions:

$\frac{1 + \cos^2 \theta}{\sin^2 \theta} - \frac{\sin^2 \theta}{\sin^2 \theta} = \frac{1 + \cos^2 \theta - \sin^2 \theta}{\sin^2 \theta}$

Applying the Pythagorean Identity Once More

We can simplify the expression further by applying the Pythagorean identity once more:

$\frac{1 + \cos^2 \theta - \sin^2 \theta}{\sin^2 \theta} = \frac{1 + \cos^2 \theta - (1 - \cos^2 \theta)}{\sin^2 \theta}$

Simplifying the Expression

We can simplify the expression further by combining the terms:

$\frac{1 + \cos^2 \theta - (1 - \cos^2 \theta)}{\sin^2 \theta} = \frac{1 + \cos^2 \theta - 1 + \cos^2 \theta}{\sin^2 \theta}$

Simplifying the Expression

We can simplify the expression further by combining the terms:

$\frac{1 + \cos^2 \theta - 1 + \cos^2 \theta}{\sin^2 \theta} = \frac{2\cos^2 \theta}{\sin^2 \theta}$

Simplifying the Expression

We can simplify the expression further by rewriting it in terms of cotangent:

$\frac{2\cos^2 \theta}{\sin^2 \theta} = \frac{2\left(\frac{\cos \theta}{\sin \theta}\right)^2}{\left(\frac{1}{\sin \theta}\right)^2}$

Simplifying the Expression

We can simplify the expression further by canceling out the common terms:

$\frac{2\left(\frac{\cos \theta}{\sin \theta}\right)^2}{\left(\frac{1}{\sin \theta}\right)^2} = 2\cot^2 \theta$

Conclusion

In conclusion, the simplified expression is $2\cot^2 \theta$ . Therefore, the correct answer is:

C. $\boxed{2 \cot^2 \theta}$

Discussion

This problem requires a deep understanding of trigonometric functions and their relationships. The key to solving this problem is to use the definitions of cosecant and cotangent functions and to apply the Pythagorean identity repeatedly. The final answer is $2\cot^2 \theta$ , which is a fundamental identity in trigonometry.

Introduction

In our previous article, we simplified the expression $\csc^2 \theta + \cot^2 \theta - 1$ to $2\cot^2 \theta$ . However, we received many questions from readers regarding the steps involved in simplifying the expression. In this article, we will address some of the frequently asked questions (FAQs) related to this problem.

Q: What is the Pythagorean identity?

A: The Pythagorean identity is a fundamental concept in trigonometry that states $\sin^2 \theta + \cos^2 \theta = 1$ . This identity is used to simplify expressions involving trigonometric functions.

Q: How do I apply the Pythagorean identity to simplify the expression?

A: To apply the Pythagorean identity, you need to rewrite the expression in terms of sine and cosine. Then, you can use the identity to simplify the expression. In this case, we rewrote the expression as $\frac{1 + \cos^2 \theta}{\sin^2 \theta} - 1$ and then applied the Pythagorean identity to simplify it further.

Q: What is the difference between $\csc^2 \theta$ and $\frac{1}{\sin^2 \theta}$ ?

A: $\csc^2 \theta$ and $\frac{1}{\sin^2 \theta}$ are equivalent expressions. The cosecant function is defined as the reciprocal of the sine function, i.e., $\csc \theta = \frac{1}{\sin \theta}$ . Therefore, $\csc^2 \theta$ is equal to $\frac{1}{\sin^2 \theta}$ .

Q: How do I simplify expressions involving cotangent?

A: To simplify expressions involving cotangent, you need to use the definition of cotangent, which is $\cot \theta = \frac{\cos \theta}{\sin \theta}$ . Then, you can rewrite the expression in terms of sine and cosine and apply the Pythagorean identity to simplify it further.

Q: What is the final answer to the problem?

A: The final answer to the problem is $2\cot^2 \theta$ . This is the simplified expression that we obtained by applying the Pythagorean identity and using the definitions of cosecant and cotangent functions.

Q: Can I use other trigonometric identities to simplify the expression?

A: Yes, you can use other trigonometric identities to simplify the expression. However, the Pythagorean identity is the most commonly used identity in this type of problem. You can also use other identities such as the sum and difference formulas, but they are not necessary in this case.

Q: How do I practice simplifying expressions involving trigonometric functions?

A: To practice simplifying expressions involving trigonometric functions, you can try solving problems like this one. You can also use online resources such as Khan Academy, MIT OpenCourseWare, and Wolfram Alpha to practice and learn more about trigonometry.

Conclusion

In conclusion, simplifying expressions involving trigonometric functions requires a deep understanding of the definitions of these functions and the Pythagorean identity. By applying the Pythagorean identity and using the definitions of cosecant and cotangent functions, we can simplify expressions like $\csc^2 \theta + \cot^2 \theta - 1$ to $2\cot^2 \theta$ . We hope that this article has helped you to understand the steps involved in simplifying this expression and has provided you with a better understanding of trigonometry.

Additional Resources

Khan Academy: Trigonometry
MIT OpenCourseWare: Trigonometry
Wolfram Alpha: Trigonometry
Mathway: Trigonometry

Discussion

We hope that this article has been helpful in addressing some of the frequently asked questions related to simplifying expressions involving trigonometric functions. If you have any further questions or need additional help, please don't hesitate to ask. We are here to help you learn and understand trigonometry.