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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.6.139a

[Technology Exercise] In Exercises 139–141, find the domain and range of each composite function. Then graph the compositions on separate screens. Do the graphs make sense in each case? Give reasons for your answers. Comment on any differences you see.
139. a. y=arctan(tan x)

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1
Identify the inner and outer functions in the composition. Here, the inner function is \(\tan x\) and the outer function is \(\arctan y\), where \(y = \tan x\).
Recall the domain and range of each function separately: \(\tan x\) has domain \(x \neq \frac{\pi}{2} + k\pi\), \(k \in \mathbb{Z}\), and range \((-\infty, \infty)\); \(\arctan x\) has domain \((-\infty, \infty)\) and range \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\).
Since \(\arctan\) is applied to \(\tan x\), the domain of the composite function \(y = \arctan(\tan x)\) is the domain of \(\tan x\), which excludes points where \(\tan x\) is undefined.
The range of the composite function is limited by the range of \(\arctan\), so \(y\) will lie in \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\).
Consider the behavior of \(\arctan(\tan x)\) over intervals where \(\tan x\) is continuous and increasing. The function essentially 'wraps' \(x\) back into the principal range of \(\arctan\), causing a periodic 'sawtooth' pattern. This explains why the graph repeats and why the range is restricted.

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