Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 5 - Section 5.4 - More Trigonometric Graphs - 5.4 Exercises - Page 439: 65

Answer

$tan(x - \frac{\pi}{2}) = -cot ~x$ $sec(x - \frac{\pi}{2}) = csc ~x$

Work Step by Step

We can use figure 5 to see why the following formulas are true. The graph of $tan(x - \frac{\pi}{2})$ is the graph of $tan~x$ shifted horizontally to the right by $\frac{\pi}{2}$ Then the vertical asymptotes are located at $x = \pi~n,$ where $n$ is an integer. The points where $tan(x - \frac{\pi}{2}) = 0$ have the form $x = \frac{\pi}{2}+\pi n$ We can see that this closely matches up with the graph of $cot~x$ except that we need to flip the graph of $cot~x$ about the x axis in order to match up perfectly. Therefore, $tan(x - \frac{\pi}{2}) = -cot ~x$ The graph of $sec(x - \frac{\pi}{2})$ is the graph of $sec~x$ shifted horizontally to the right by $\frac{\pi}{2}$ Then the vertical asymptotes are located at $x = \pi~n,$ where $n$ is an integer. The points where $sec(x - \frac{\pi}{2}) = 1$ have the form $x = \frac{\pi}{2}+\pi n$ We can see that the graph of $sec(x - \frac{\pi}{2})$ matches up perfectly with the graph of $csc~x$ Therefore, $sec(x - \frac{\pi}{2}) = csc ~x$
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