S. D. V. Stephens

notes / Integrated Mathematics / chapter 12: Precalculus (Art of Problem Solving)

2a Practice: Trigonometric Equations and Triangles

Sinusoids and algebra

For :

Example 2a.1. Solve .

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Then and , giving the points and . Check: and .

Example 2a.2. Solve .

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Setting this equal to and squaring: Cancelling : so or .

Law of cosines

Theorem 2a.3 (Law of cosines). where is the angle between sides and , opposite side (for example, sides and with between them).

Example 2a.4. Find if .

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Next: .

Law of sines

Example 2a.5. A triangle has angles , and , with side opposite the angle. Find the side opposite .

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with .

Example 2a.6. Find if .

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A sketch of the sine curve meets the height twice: both angles work.

Next: .

Solving trigonometric equations

Note. Rule of note: when arc… (it is at a peak), it will only have one solution (per period).

Example 2a.7. Solve .

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Since , there are two families:

Example 2a.8. Solve .

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Example 2a.9. Solve .

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Example 2a.10. Solve .

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Example 2a.11. Solve cm.

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Angle addition and double angles

Theorem 2a.12.

With the values and :

Since :