Double-angle Formulas (d) sin 20 = 2 sin cos 0 (e) cos 20 (f) tan 20 = cos²0-sin² 0 = 1-2 sin² 0 = 2 cos² 0 - 1 2 tan²0 1-tan²0

Calculus: Early Transcendentals
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Author:James Stewart
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Chapter1: Functions And Models
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Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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**Algebra of Trigonometry**

**Double-angle Formulas**

1. \(\sin 2\theta = 2 \sin \theta \cos \theta\)
2. \(\cos 2\theta = \cos^2 \theta - \sin^2 \theta = 1 - 2 \sin^2 \theta = 2 \cos^2 \theta - 1\)
3. \(\tan 2\theta = \frac{2 \tan^2 \theta}{1 - \tan^2 \theta}\)
4. Derive the formula of \(\cos 4\theta\)

The provided text includes several common double-angle trigonometric formulas, which are important for simplifying and solving trigonometric equations. Let's go through the details of each formula:

1. **Sine Double Angle Formula:**
   \[\sin 2\theta = 2 \sin \theta \cos \theta\]
   This formula expresses the sine of double an angle in terms of the sine and cosine of the angle.

2. **Cosine Double Angle Formulas:**
   \[\cos 2\theta = \cos^2 \theta - \sin^2 \theta\]
   This primary formula for \(\cos 2\theta\) can be further expanded into two equivalent forms depending on the known values:
   \[\cos 2\theta = 1 - 2 \sin^2 \theta\]
   \[\cos 2\theta = 2 \cos^2 \theta - 1\]
   
   These various forms can be used based on which trigonometric values are more convenient or known in a problem.

3. **Tangent Double Angle Formula:**
   \[\tan 2\theta = \frac{2 \tan^2 \theta}{1 - \tan^2 \theta}\]
   This formula provides the tangent of double an angle in terms of the tangent of the angle. It is particularly useful when working with angles derived from tangent functions.

4. **Deriving the Formula for \(\cos 4\theta\):**
   This step prompts the derivation of the formula for the cosine of four times an angle (\(4\theta\)) based on the given double-angle formulas. This derivation process involves using the double-angle formula for cosine repeatedly to express \(\cos 4\theta\) in terms of \
Transcribed Image Text:**Algebra of Trigonometry** **Double-angle Formulas** 1. \(\sin 2\theta = 2 \sin \theta \cos \theta\) 2. \(\cos 2\theta = \cos^2 \theta - \sin^2 \theta = 1 - 2 \sin^2 \theta = 2 \cos^2 \theta - 1\) 3. \(\tan 2\theta = \frac{2 \tan^2 \theta}{1 - \tan^2 \theta}\) 4. Derive the formula of \(\cos 4\theta\) The provided text includes several common double-angle trigonometric formulas, which are important for simplifying and solving trigonometric equations. Let's go through the details of each formula: 1. **Sine Double Angle Formula:** \[\sin 2\theta = 2 \sin \theta \cos \theta\] This formula expresses the sine of double an angle in terms of the sine and cosine of the angle. 2. **Cosine Double Angle Formulas:** \[\cos 2\theta = \cos^2 \theta - \sin^2 \theta\] This primary formula for \(\cos 2\theta\) can be further expanded into two equivalent forms depending on the known values: \[\cos 2\theta = 1 - 2 \sin^2 \theta\] \[\cos 2\theta = 2 \cos^2 \theta - 1\] These various forms can be used based on which trigonometric values are more convenient or known in a problem. 3. **Tangent Double Angle Formula:** \[\tan 2\theta = \frac{2 \tan^2 \theta}{1 - \tan^2 \theta}\] This formula provides the tangent of double an angle in terms of the tangent of the angle. It is particularly useful when working with angles derived from tangent functions. 4. **Deriving the Formula for \(\cos 4\theta\):** This step prompts the derivation of the formula for the cosine of four times an angle (\(4\theta\)) based on the given double-angle formulas. This derivation process involves using the double-angle formula for cosine repeatedly to express \(\cos 4\theta\) in terms of \
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