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Ch. 1 - Angles and the Trigonometric Functions
Blitzer - Trigonometry 3rd Edition
Blitzer3rd EditionTrigonometryISBN: 9780137316601Non è quello che usi tu?Cambia libro di testo
Capitolo 1, Problema 6

In Exercises 1–8, a point on the terminal side of angle θ is given. Find the exact value of each of the six trigonometric functions of θ. (5, -5)

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Identify the coordinates of the point on the terminal side of angle \( \theta \). Here, the point is \( (5, -5) \), so \( x = 5 \) and \( y = -5 \).
Calculate the radius \( r \), which is the distance from the origin to the point, using the formula \( r = \sqrt{x^2 + y^2} \). Substitute the values to get \( r = \sqrt{5^2 + (-5)^2} \).
Recall the definitions of the six trigonometric functions in terms of \( x \), \( y \), and \( r \): \[ \sin \theta = \frac{y}{r}, \quad \cos \theta = \frac{x}{r}, \quad \tan \theta = \frac{y}{x}, \quad \csc \theta = \frac{r}{y}, \quad \sec \theta = \frac{r}{x}, \quad \cot \theta = \frac{x}{y} \]
Substitute the values of \( x \), \( y \), and \( r \) into each of the six functions to express them exactly in terms of radicals and integers.
Simplify each expression if possible, keeping in mind the signs of \( x \), \( y \), and \( r \) to determine the correct sign of each trigonometric function.

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Coordinates and the Terminal Side of an Angle

The terminal side of an angle θ in standard position passes through a point (x, y). This point helps determine the angle's trigonometric values by relating x and y to the radius (r), which is the distance from the origin to the point, calculated using the Pythagorean theorem.
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Definition of the Six Trigonometric Functions

The six trigonometric functions—sine, cosine, tangent, cosecant, secant, and cotangent—are ratios involving x, y, and r. Specifically, sin(θ) = y/r, cos(θ) = x/r, tan(θ) = y/x, and their reciprocals define the other three functions. These ratios are essential for finding exact values.
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Sign of Trigonometric Functions Based on Quadrants

The signs of x, y, and r determine the sign of each trigonometric function. Since r is always positive, the signs depend on the quadrant where the point lies. For (5, -5), the point is in the fourth quadrant, affecting the positivity or negativity of sine, cosine, and tangent values.
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