1+ cos 20 Show that cos 0

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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Verify using proofs

**Trigonometric Identity Proof**

The image presents a trigonometric identity that needs to be proven:

\[ \cos^2 \theta = \frac{1 + \cos 2\theta}{2} \]

**Explanation:**

This identity relates the square of the cosine of an angle (\(\theta\)) to the cosine of twice that angle (\(2\theta\)). It is a commonly used identity in trigonometry known as the "Power-Reduction Formulas." These formulas are useful for simplifying expressions involving trigonometric functions to make integration or equation-solving more manageable.

**Proof Overview:**

To prove this identity, we can start by using the double-angle formula for cosine:
\[ \cos 2\theta = 2\cos^2 \theta - 1 \]

Rearrange the formula to express \(\cos^2 \theta\):
\[ 2\cos^2 \theta = 1 + \cos 2\theta \]

Now, divide both sides by 2:
\[ \cos^2 \theta = \frac{1 + \cos 2\theta}{2} \]

This completes the proof, verifying the identity as shown in the equation.
Transcribed Image Text:**Trigonometric Identity Proof** The image presents a trigonometric identity that needs to be proven: \[ \cos^2 \theta = \frac{1 + \cos 2\theta}{2} \] **Explanation:** This identity relates the square of the cosine of an angle (\(\theta\)) to the cosine of twice that angle (\(2\theta\)). It is a commonly used identity in trigonometry known as the "Power-Reduction Formulas." These formulas are useful for simplifying expressions involving trigonometric functions to make integration or equation-solving more manageable. **Proof Overview:** To prove this identity, we can start by using the double-angle formula for cosine: \[ \cos 2\theta = 2\cos^2 \theta - 1 \] Rearrange the formula to express \(\cos^2 \theta\): \[ 2\cos^2 \theta = 1 + \cos 2\theta \] Now, divide both sides by 2: \[ \cos^2 \theta = \frac{1 + \cos 2\theta}{2} \] This completes the proof, verifying the identity as shown in the equation.
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