Chapter 5: Problem 127
Find the five remaining trigonometric finction values for each angle. \(\tan \theta=-\frac{15}{8},\) and \(\theta\) is in quadrant II.
Short Answer
Expert verified
\( \sin \theta = \frac{15}{17}, \cos \theta = \frac{-8}{17}, \csc \theta = \frac{17}{15}, \sec \theta = -\frac{17}{8}, \cot \theta = -\frac{8}{15} \)
Step by step solution
01
- Identify the Given Information
It is given that \(\tan \theta = -\frac{15}{8} \) and \( \theta \) is in quadrant II. Note that in quadrant II, sine is positive, cosine is negative, and tangent is negative.
02
- Compute the Hypotenuse
Use the Pythagorean identity to find the hypotenuse \( r \). Let the opposite side be \( y = 15 \) and the adjacent side be \( x = -8 \) (keeping track of signs in quadrant II).\[ r = \sqrt{x^2 + y^2} = \sqrt{(-8)^2 + 15^2} = \sqrt{64 + 225} = \sqrt{289} = 17 \]
03
- Compute Sine
Use the definition of sine: \(\frac{\text{opposite}}{\text{hypotenuse}} = \frac{y}{r} \).\[ \sin \theta = \frac{15}{17} \]
04
- Compute Cosine
Use the definition of cosine: \(\frac{\text{adjacent}}{\text{hypotenuse}} = \frac{x}{r} \).\[ \cos \theta = \frac{-8}{17} \]
05
- Compute Cosecant
The cosecant is the reciprocal of sine: \(\frac{1}{\text{sin}} \).\[ \csc \theta = \frac{1}{\frac{15}{17}}= \frac{17}{15} \]
06
- Compute Secant
The secant is the reciprocal of cosine: \(\frac{1}{\text{cos}} \).\[ \sec \theta = \frac{1}{\frac{-8}{17}} = -\frac{17}{8} \]
07
- Compute Cotangent
The cotangent is the reciprocal of tangent: \(\frac{1}{\text{tan}} \).\[ \cot \theta = \frac{1}{-\frac{15}{8}} = -\frac{8}{15} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
tangent
The tangent of an angle in a right triangle is the ratio of the length of the opposite side to the length of the adjacent side. It is represented as: \(\tan \theta = \frac{\text{opposite}}{\text{adjacent}} \). In the given problem, \(\tan \theta = -\frac{15}{8}\). This ratio helps us find other trigonometric functions based on the given angle.
quadrant II
In the coordinate system, each quadrant has specific signs for trigonometric functions. In quadrant II:
- Sine is positive,
- Cosine is negative,
- Tangent is negative.
Pythagorean identity
The Pythagorean identity is a fundamental relation in trigonometry. It states: \[ \text{sin}^2 \theta + \text{cos}^2 \theta = 1 \]. Using this identity helps us find the hypotenuse when we know the opposite and adjacent sides. In the problem, we find the hypotenuse as: \[ r = \sqrt{x^2 + y^2} = 17 \].
sine
Sine of an angle is defined as the ratio of the length of the opposite side to the hypotenuse: \(\text{sin} \theta = \frac{\text{opposite}}{\text{hypotenuse}}\). For our problem, with the opposite side at 15 and hypotenuse at 17:
\[ \text{sin} \theta = \frac{15}{17} \].
\[ \text{sin} \theta = \frac{15}{17} \].
cosine
Cosine of an angle is the ratio of the length of the adjacent side to the hypotenuse: \(\text{cos} \theta = \frac{\text{adjacent}}{\text{hypotenuse}}\). Here, with the adjacent side of -8 and hypotenuse of 17:
\[ \text{cos} \theta = \frac{-8}{17} \].
\[ \text{cos} \theta = \frac{-8}{17} \].
cosecant
Cosecant is the reciprocal of sine: \(\text{csc} \theta = \frac{1}{\text{sin} \theta}\). For the given problem:
\[ \text{csc} \theta = \frac{1}{\frac{15}{17}} = \frac{17}{15} \]. It helps us understand sine in terms of its reciprocal value.
\[ \text{csc} \theta = \frac{1}{\frac{15}{17}} = \frac{17}{15} \]. It helps us understand sine in terms of its reciprocal value.
secant
Secant is the reciprocal of cosine: \(\text{sec} \theta = \frac{1}{\text{cos} \theta}\). For \(\theta\) in our problem:
\[ \text{sec} \theta = \frac{1}{\frac{-8}{17}} = -\frac{17}{8} \]. This reciprocal relationship helps in comprehending the negative value of cosine.
\[ \text{sec} \theta = \frac{1}{\frac{-8}{17}} = -\frac{17}{8} \]. This reciprocal relationship helps in comprehending the negative value of cosine.
cotangent
Cotangent is defined as the reciprocal of tangent: \(\text{cot} \theta = \frac{1}{\text{tan} \theta}\). Considering the provided \(\tan \theta = -\frac{15}{8}\):
\[ \text{cot} \theta = \frac{1}{-\frac{15}{8}} = -\frac{8}{15} \]. Using cotangent helps in further confirming the negative tangent value.
\[ \text{cot} \theta = \frac{1}{-\frac{15}{8}} = -\frac{8}{15} \]. Using cotangent helps in further confirming the negative tangent value.