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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 54

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 . See Example 3. ―5x ― 3y = 0 , x ≤ 0

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1
Rewrite the given equation of the terminal side in slope-intercept form to understand the line better. Starting with \(-5x - 3y = 0\), solve for \(y\) to get \(y = -\frac{5}{3}x\).
Since the terminal side is a ray starting from the origin (standard position), and the restriction is \(x \leq 0\), focus on the portion of the line where \(x\) is non-positive (to the left of the origin).
Determine the angle \(\theta\) that this terminal side makes with the positive x-axis. Recall that the slope \(m\) of the line is related to the angle by \(m = \tan(\theta)\). Here, \(m = -\frac{5}{3}\), so \(\theta = \arctan\left(-\frac{5}{3}\right)\).
Since \(x \leq 0\), the terminal side lies in either the second or third quadrant. Adjust the angle \(\theta\) accordingly to find the least positive angle in standard position that corresponds to this ray.
Once \(\theta\) is identified, use the definitions of the six trigonometric functions in terms of \(x\) and \(y\) coordinates on the terminal side: \(\sin \theta = \frac{y}{r}\), \(\cos \theta = \frac{x}{r}\), \(\tan \theta = \frac{y}{x}\), \(\csc \theta = \frac{r}{y}\), \(\sec \theta = \frac{r}{x}\), and \(\cot \theta = \frac{x}{y}\), where \(r = \sqrt{x^2 + y^2}\). Substitute values consistent with the line and restriction to find these ratios.

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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 counterclockwise 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 the Terminal Side

The terminal side of the angle lies along a line described by the equation -5x - 3y = 0. Rearranging this gives the slope, which corresponds to the tangent of the angle θ. The restriction x ≤ 0 limits the terminal side to a specific half-plane, affecting the angle's quadrant and thus the sign of trigonometric functions.
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Categorizing Linear Equations

Six Trigonometric Functions and Their Calculation

The six trigonometric functions (sin, cos, tan, csc, sec, cot) are ratios of the sides of a right triangle formed by the terminal side and the coordinate axes. Once θ is identified, these functions can be found using the coordinates of a point on the terminal side, considering the quadrant to assign correct signs.
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How to Use a Calculator for Trig Functions