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Ch. 1 - Trigonometric Functions
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 35

An equation of the terminal side of an angle θ in standard position is given with a restriction on x. Sketch the least positive such angle θ , and find the values of the six trigonometric functions of θ . 12x + 5y = 0 , x ≥ 0 .

Guida verificata passo dopo passo
1
Rewrite the given equation of the terminal side in slope-intercept form to understand the line better. Starting with \(12x + 5y = 0\), solve for \(y\) to get \(y = -\frac{12}{5}x\).
Recognize that the terminal side of angle \(\theta\) lies along the line \(y = -\frac{12}{5}x\) with the restriction \(x \geq 0\). This means the terminal side is in the fourth quadrant or on the positive x-axis.
Find the reference angle \(\alpha\) by considering the slope as the tangent of the angle the line makes with the positive x-axis. Use \(\tan(\alpha) = \left| -\frac{12}{5} \right| = \frac{12}{5}\), then find \(\alpha = \arctan\left(\frac{12}{5}\right)\).
Determine the least positive angle \(\theta\) in standard position. Since the line is in the fourth quadrant (because \(x \geq 0\) and \(y\) is negative), calculate \(\theta = 2\pi - \alpha\) (in radians) or \(360^\circ - \alpha\) (in degrees).
Calculate the six trigonometric functions of \(\theta\) by first choosing a point on the terminal side that satisfies the line equation and \(x \geq 0\). For example, use \(x = 5\), then \(y = -12\). Compute the hypotenuse \(r = \sqrt{x^2 + y^2} = \sqrt{5^2 + (-12)^2}\). Then use the definitions: \(\sin \theta = \frac{y}{r}\), \(\cos \theta = \frac{x}{r}\), \(\tan \theta = \frac{y}{x}\), \(\csc \theta = \frac{r}{y}\), \(\sec \theta = \frac{r}{x}\), and \(\cot \theta = \frac{x}{y}\).

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Standard Position of an Angle

An angle in standard position has its vertex at the origin and its initial side along the positive x-axis. The terminal side is determined by rotating the initial side by the angle θ. Understanding this helps in visualizing and sketching the angle based on the given line equation.
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Drawing Angles in Standard Position

Equation of a Line and Its Relation to an Angle

The equation 12x + 5y = 0 represents a line through the origin. The slope of this line corresponds to the tangent of the angle θ formed by the terminal side with the positive x-axis. The restriction x ≥ 0 limits the terminal side to the right half-plane, ensuring the angle is the least positive angle.
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Introduction to Parametric Equations

Six Trigonometric Functions

The six trigonometric functions—sine, cosine, tangent, cosecant, secant, and cotangent—are ratios of the sides of a right triangle or coordinates on the unit circle. Once θ is identified, these functions can be calculated using the coordinates of a point on the terminal side or the slope of the line.
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