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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.6.19

Find the limits in Exercises 13–20. (If in doubt, look at the function’s graph.)
19. lim(x→∞)arccsc(x)

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1
Recall the definition of the function involved: \(\arccsc(x)\) is the inverse cosecant function, which gives the angle \(\theta\) such that \(\csc(\theta) = x\).
Understand the domain and range of \(\arccsc(x)\): the domain is \((-\infty, -1] \cup [1, \infty)\), and the range is \([-\frac{\pi}{2}, 0) \cup (0, \frac{\pi}{2}]\) excluding zero.
Analyze the behavior of \(\arccsc(x)\) as \(x\) approaches infinity: since \(\csc(\theta) = \frac{1}{\sin(\theta)}\), large values of \(x\) correspond to \(\sin(\theta)\) approaching zero from the positive side.
Determine the angle \(\theta\) whose cosecant is very large positive: this angle approaches \(0\) from the positive side, because \(\csc(\theta)\) becomes large when \(\sin(\theta)\) is close to zero but positive.
Conclude that \(\lim_{x \to \infty} \arccsc(x)\) approaches \(0\) from the positive side, so the limit is \(0^+\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Limit of a Function as x Approaches Infinity

This concept involves finding the value that a function approaches as the input variable x grows without bound. Understanding limits at infinity helps determine the end behavior of functions, which is crucial for analyzing asymptotic behavior and horizontal asymptotes.
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Arccsc(x) is the inverse cosecant function, which returns the angle whose cosecant is x. Its domain is |x| ≥ 1, and its range is typically restricted to [-π/2, 0) ∪ (0, π/2]. Knowing the properties and domain of arccsc is essential for evaluating limits involving this function.
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Behavior of Arccsc(x) as x Approaches Infinity

As x approaches infinity, arccsc(x) approaches the angle whose cosecant is infinitely large, which corresponds to an angle approaching 0 from the positive side. Understanding this behavior allows one to evaluate the limit by relating large values of x to the corresponding angle values.
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