Precalculus (6th Edition) Blitzer

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

Chapter 4 - Section 4.4 - Trigonometric Functions of Any Angle - Exercise Set - Page 575: 4

Answer

The six trigonometric functions of $\theta $ for point $\left( 3,7 \right)$ are, $\sin \theta =\frac{7\sqrt{58}}{58},\cos \theta =\frac{3\sqrt{58}}{58},\tan \theta =\frac{7}{3},\csc \theta =\frac{\sqrt{58}}{7},\sec \theta =\frac{\sqrt{58}}{3}$ and $\cot \theta =\frac{3}{7}$.

Work Step by Step

Consider the point $\left( 3,7 \right)$. Here, $x=3$ and $y=7$ The six trigonometric functions of $\theta $ are defined in the term of ratios. According to the Pythagoras theorem, the hypotenuse is, $r=\sqrt{{{x}^{2}}+{{y}^{2}}}$ Substitute $3$ for $x$ and $7$ for $y$. $\begin{align} & r=\sqrt{{{\left( 3 \right)}^{2}}+{{\left( 7 \right)}^{2}}} \\ & =\sqrt{9+49} \\ & =\sqrt{58} \end{align}$ Write the trigonometric expression of $\sin \theta $. $\sin \theta =\frac{y}{r}$ Substitute $7$ for $y$ and $\sqrt{58}$ for $r$. $\begin{align} & \sin \theta =\frac{7}{\sqrt{58}} \\ & =\frac{7}{\sqrt{58}}.\frac{\sqrt{58}}{\sqrt{58}} \\ & =\frac{7\sqrt{58}}{58} \end{align}$ Recall the trigonometric expression of $\cos \theta $. $\cos \theta =\frac{x}{r}$ Substitute $3$ for $x$ and $\sqrt{58}$ for $r$. $\begin{align} & \cos \theta =\frac{3}{\sqrt{58}} \\ & =\frac{3}{\sqrt{58}}.\frac{\sqrt{58}}{\sqrt{58}} \\ & =\frac{3\sqrt{58}}{58} \end{align}$ Recall the trigonometric expression of $\tan \theta $. $\tan \theta =\frac{y}{x}$ Substitute $3$ for $x$ and $7$ for $y$. $\tan \theta =\frac{7}{3}$ Recall the trigonometric expression of $\csc \theta $. $\csc \theta =\frac{r}{y}$ Substitute $7$ for $y$ and $\sqrt{58}$ for $r$. $\csc \theta =\frac{\sqrt{58}}{7}$ Recall the trigonometric expression of $\sec \theta $. $\sec \theta =\frac{r}{x}$ Substitute $3$ for $x$ and $\sqrt{58}$ for $r$. $\sec \theta =\frac{\sqrt{58}}{3}$ Recall the trigonometric expression of $\cot \theta $. $\cot \theta =\frac{x}{y}$ Substitute $3$ for $x$ and $7$ for $y$. $\cot \theta =\frac{3}{7}$ Thus, the six trigonometric functions of $\theta $ for point $\left( 3,7 \right)$ are, $\sin \theta =\frac{7\sqrt{58}}{58},\cos \theta =\frac{3\sqrt{58}}{58},\tan \theta =\frac{7}{3},\csc \theta =\frac{\sqrt{58}}{7},\sec \theta =\frac{\sqrt{58}}{3}$ and $\cot \theta =\frac{3}{7}$.
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