Skip to main content
Ch. 2 - Limits and Continuity
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 2.6.93

Use formal definitions to prove the limit statements in Exercises 93–96.


lim x → 0 (−1 / x²) = −∞

Guida verificata passo dopo passo
1
Understand the formal definition of a limit approaching negative infinity: For every positive number M, there exists a positive number δ such that for all x, 0 < |x| < δ implies f(x) < -M.
Identify the function f(x) = -1/x² and the limit statement lim x → 0 (−1 / x²) = −∞.
Given any positive number M, we need to find a δ > 0 such that for all x, 0 < |x| < δ, the inequality -1/x² < -M holds.
Rearrange the inequality -1/x² < -M to 1/x² > M, which implies x² < 1/M. Therefore, |x| < 1/√M.
Choose δ = 1/√M. Then, for all x such that 0 < |x| < δ, it follows that 1/x² > M, which satisfies the condition for the limit to be -∞.

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.
Durata del video:
3m

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

Limit Definition

The formal definition of a limit involves showing that for every ε > 0, there exists a δ > 0 such that if 0 < |x - c| < δ, then |f(x) - L| < ε. In this case, the limit is approaching negative infinity, which requires a modified approach to demonstrate that f(x) becomes arbitrarily large negative as x approaches 0.
Video consigliato:
Percorso guidato
05:43
Definition of the Definite Integral

Behavior of Rational Functions

Understanding the behavior of rational functions, particularly as x approaches a value where the denominator tends to zero, is crucial. For the function −1/x², as x approaches 0, the denominator becomes very small, causing the function value to grow negatively without bound, leading to a limit of negative infinity.
Video consigliato:
6:04
Intro to Rational Functions

Infinity in Limits

When dealing with limits that approach infinity, the concept of infinity in calculus is used to describe unbounded behavior. A limit approaching negative infinity means the function values decrease without bound as x approaches the specified point. This requires demonstrating that for any large negative number, the function can be made smaller than that number by choosing x sufficiently close to the limit point.
Video consigliato:
03:07
Cases Where Limits Do Not Exist