cot(x) cot(y) + 1 cot(y) – cot(x) cot(x – y) =
Trigonometry (11th Edition)
11th Edition
ISBN:9780134217437
Author:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Publisher:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Chapter1: Trigonometric Functions
Section: Chapter Questions
Problem 1RE:
1. Give the measures of the complement and the supplement of an angle measuring 35°.
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![### Proving the Identity in Trigonometry
We are given the following trigonometric identity to prove:
\[ \cot(x - y) = \frac{\cot(x) \cdot \cot(y) + 1}{\cot(y) - \cot(x)} \]
We'll prove this identity by using reciprocal identities and subtraction formulas step by step.
#### Step 1: Use a Reciprocal Identity, and then use a Subtraction Formula.
Starting with the left-hand side:
\[ \cot(x - y) = \frac{1}{\tan(x - y)} \]
Using the tangent subtraction formula:
\[ \tan(x - y) = \frac{\tan(x) - \tan(y)}{1 + \tan(x) \cdot \tan(y)}\]
So by reciprocal identity:
\[ \cot(x - y) = \frac{1}{\frac{\tan(x) - \tan(y)}{1 + \tan(x) \cdot \tan(y)}} \]
\[ = \frac{1 + \tan(x) \cdot \tan(y)}{\tan(x) - \tan(y)} \]
#### Step 2: Use a Reciprocal Identity, and simplify the compound fraction.
Next, express tangents in terms of cotangents:
\[ \tan(x) = \frac{1}{\cot(x)}, \quad \tan(y) = \frac{1}{\cot(y)} \]
Substituting these into the equation:
\[ \cot(x - y) = \frac{1 + \frac{1}{\cot(x)} \cdot \frac{1}{\cot(y)}}{\frac{1}{\cot(x)} - \frac{1}{\cot(y)}} \]
Simplifying the numerator and the denominator:
\[ = \frac{1 + \frac{1}{\cot(x) \cdot \cot(y)}}{\frac{1}{\cot(x)} - \frac{1}{\cot(y)}} \]
\[ = \frac{1 + \frac{1}{\cot(x) \cot(y)}}{\frac{\cot(y) - \cot(x)}{\cot(x) \cdot \cot(y)}} \]
Further simplify to:
\[ = \frac{(1 + \frac{1}{\cot(x) \cdot \cot(y)}) \cdot (\cot(x) \cdot \cot(y))}{](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbd285f6f-67ec-4ffa-8e9b-700f12fa780d%2Faaf2f727-0286-4e44-a403-dea2cf178d26%2Fcvwh6d.jpeg&w=3840&q=75)
Transcribed Image Text:### Proving the Identity in Trigonometry
We are given the following trigonometric identity to prove:
\[ \cot(x - y) = \frac{\cot(x) \cdot \cot(y) + 1}{\cot(y) - \cot(x)} \]
We'll prove this identity by using reciprocal identities and subtraction formulas step by step.
#### Step 1: Use a Reciprocal Identity, and then use a Subtraction Formula.
Starting with the left-hand side:
\[ \cot(x - y) = \frac{1}{\tan(x - y)} \]
Using the tangent subtraction formula:
\[ \tan(x - y) = \frac{\tan(x) - \tan(y)}{1 + \tan(x) \cdot \tan(y)}\]
So by reciprocal identity:
\[ \cot(x - y) = \frac{1}{\frac{\tan(x) - \tan(y)}{1 + \tan(x) \cdot \tan(y)}} \]
\[ = \frac{1 + \tan(x) \cdot \tan(y)}{\tan(x) - \tan(y)} \]
#### Step 2: Use a Reciprocal Identity, and simplify the compound fraction.
Next, express tangents in terms of cotangents:
\[ \tan(x) = \frac{1}{\cot(x)}, \quad \tan(y) = \frac{1}{\cot(y)} \]
Substituting these into the equation:
\[ \cot(x - y) = \frac{1 + \frac{1}{\cot(x)} \cdot \frac{1}{\cot(y)}}{\frac{1}{\cot(x)} - \frac{1}{\cot(y)}} \]
Simplifying the numerator and the denominator:
\[ = \frac{1 + \frac{1}{\cot(x) \cdot \cot(y)}}{\frac{1}{\cot(x)} - \frac{1}{\cot(y)}} \]
\[ = \frac{1 + \frac{1}{\cot(x) \cot(y)}}{\frac{\cot(y) - \cot(x)}{\cot(x) \cdot \cot(y)}} \]
Further simplify to:
\[ = \frac{(1 + \frac{1}{\cot(x) \cdot \cot(y)}) \cdot (\cot(x) \cdot \cot(y))}{
![**Verify the Identity**
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} = 2 \sec(x) \]
To verify this trigonometric identity, we start by considering the left-hand side:
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} \]
First, find a common denominator:
\[ \frac{\sec(x) - \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} + \frac{\sec(x) + \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} \]
Combine the fractions:
\[ \frac{\sec(x) - \tan(x) + \sec(x) + \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} \]
Simplify the numerator:
\[ \frac{\sec(x) + \sec(x)}{\sec^2(x) - \tan^2(x)} \]
\[ \frac{2 \sec(x)}{\sec^2(x) - \tan^2(x)} \]
Noting that:
\[ \sec^2(x) - \tan^2(x) = 1 \]
The expression becomes:
\[ \frac{2 \sec(x)}{1} = 2 \sec(x) \]
Thus, we have shown that:
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} = 2 \sec(x) \]
This verifies the given identity.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbd285f6f-67ec-4ffa-8e9b-700f12fa780d%2Faaf2f727-0286-4e44-a403-dea2cf178d26%2F9mvii2q.jpeg&w=3840&q=75)
Transcribed Image Text:**Verify the Identity**
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} = 2 \sec(x) \]
To verify this trigonometric identity, we start by considering the left-hand side:
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} \]
First, find a common denominator:
\[ \frac{\sec(x) - \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} + \frac{\sec(x) + \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} \]
Combine the fractions:
\[ \frac{\sec(x) - \tan(x) + \sec(x) + \tan(x)}{(\sec(x) + \tan(x))(\sec(x) - \tan(x))} \]
Simplify the numerator:
\[ \frac{\sec(x) + \sec(x)}{\sec^2(x) - \tan^2(x)} \]
\[ \frac{2 \sec(x)}{\sec^2(x) - \tan^2(x)} \]
Noting that:
\[ \sec^2(x) - \tan^2(x) = 1 \]
The expression becomes:
\[ \frac{2 \sec(x)}{1} = 2 \sec(x) \]
Thus, we have shown that:
\[ \frac{1}{\sec(x) + \tan(x)} + \frac{1}{\sec(x) - \tan(x)} = 2 \sec(x) \]
This verifies the given identity.
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