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Ch. 6 - Inverse Circular Functions and Trigonometric Equations
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161당신이 사용하는 게 아니라요?교과서 변경
7장, 문제 6.3.41

Solve each equation (x in radians and θ in degrees) for all exact solutions where appropriate. Round approximate answers in radians to four decimal places and approximate answers in degrees to the nearest tenth. Write answers using the least possible nonnegative angle measures.


2 sin θ = 2 cos 2θ

검증된 단계별 안내
1
Start by writing down the given equation: \(2 \sin \theta = 2 \cos 2\theta\).
Divide both sides of the equation by 2 to simplify it: \(\sin \theta = \cos 2\theta\).
Recall the double-angle identity for cosine: \(\cos 2\theta = 1 - 2 \sin^2 \theta\) or \(\cos 2\theta = 2 \cos^2 \theta - 1\). Choose the form that seems easiest to work with; here, using \(\cos 2\theta = 1 - 2 \sin^2 \theta\) is convenient.
Substitute the identity into the equation: \(\sin \theta = 1 - 2 \sin^2 \theta\).
Rearrange the equation to form a quadratic in \(\sin \theta\): \(2 \sin^2 \theta + \sin \theta - 1 = 0\). From here, solve for \(\sin \theta\) using the quadratic formula or factoring, then find all solutions for \(\theta\) within the specified domain, converting between radians and degrees as needed and applying the least possible nonnegative angle measures.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Trigonometric Equations and Their Solutions

Trigonometric equations involve functions like sine and cosine and require finding all angle values that satisfy the equation. Solutions often include general forms accounting for periodicity, and exact solutions use known angle values. Understanding how to isolate and solve for the variable is essential.
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How to Solve Linear Trigonometric Equations

Double-Angle Identities

Double-angle identities express trigonometric functions of twice an angle in terms of single angles, such as cos 2θ = cos²θ - sin²θ or cos 2θ = 1 - 2sin²θ. These identities help rewrite equations to a single trigonometric function, simplifying the solving process.
추천 영상:
05:06
Double Angle Identities

Angle Measurement and Conversion

Angles can be measured in degrees or radians, and problems may require answers in both units. Understanding how to convert between radians and degrees, and expressing solutions within a specified interval (usually 0 to 2π or 0° to 360°), ensures answers are correctly formatted and complete.
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Reference Angles on the Unit Circle