Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 4 - Review Exercises - Page 645: 51

Answer

The trigonometric functions are: $\sin \theta =-\frac{\sqrt{10}}{10}\text{; cos}\theta \text{=}-\frac{3\sqrt{10}}{10}\text{; tan}\theta \text{=}\frac{1}{3};\text{ csc}\theta \text{=}-\sqrt{10};\text{ sec}\theta \text{=}-\frac{\sqrt{10}}{3}$.

Work Step by Step

We know that $\cot \theta >0\text{ and cos}\theta <0$ , so $\theta $ lies in quadrant III. So, in quadrant III, x and y are both negative. Here, $\begin{align} & \cot \theta =\frac{3}{1} \\ & =\frac{x}{y} \\ & =\frac{-3}{-1} \end{align}$ Therefore, $x=-3\text{ and }y=-1$. Now, calculate r as: $\begin{align} & {{r}^{2}}={{x}^{2}}+{{y}^{2}} \\ & r=\sqrt{{{\left( -3 \right)}^{2}}+{{\left( -1 \right)}^{2}}} \\ & r=\sqrt{9+1} \\ & r=\sqrt{10} \end{align}$ Now, evaluate the sine function as follows: $\begin{align} & \sin \theta =\frac{y}{r} \\ & =\frac{-1}{\sqrt{10}} \\ & =\frac{-1\cdot \sqrt{10}}{\sqrt{10}\cdot \sqrt{10}} \\ & =-\frac{\sqrt{10}}{10} \end{align}$ Then, evaluate the cosine function as follows: $\begin{align} & \cos \theta =\frac{x}{r} \\ & =\frac{-3}{\sqrt{10}} \\ & =-\frac{3\cdot \sqrt{10}}{\sqrt{10}\cdot \sqrt{10}} \\ & =-\frac{3\sqrt{10}}{10} \end{align}$ Then, evaluate the tangent function as follows: $\begin{align} & \tan \theta =\frac{y}{x} \\ & =\frac{-1}{-3} \\ & =\frac{1}{3} \end{align}$ Then, evaluate the cosecant function as follows: $\begin{align} & \csc \theta =\frac{r}{y} \\ & =\frac{\sqrt{10}}{-1} \\ & =-\sqrt{10} \end{align}$ Finally evaluate the secant function as follows: $\begin{align} & \sec \theta =\frac{r}{x} \\ & =\frac{\sqrt{10}}{-3} \\ & =-\frac{\sqrt{10}}{3} \end{align}$
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