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AP - Calculus AB/BC:: Limits and Continuity

Created by Chat Robotics Community  ·  Updated 2026-08-30

Curriculum Overview

Topics & Key Concepts

Ap Calculus

Sample Flashcard Questions & Answers

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Question #1 Active Recall

What does the statement \(\lim_{x \to a} f(x) = L\) mean, in terms of the behavior of \(f\)?

- **A)** \(f(a) = L\) exactly, regardless of nearby values
- **B)** As \(x\) gets arbitrarily close to \(a\) (from either side, without necessarily equaling \(a\)), \(f(x)\) gets arbitrarily close to \(L\)
- **C)** \(f\) is continuous at \(a\) and equals \(L\) there
- **D)** \(f\) is differentiable at \(a\) with derivative \(L\)

Answer & Explanation:
**Answer: B)**

A limit describes the value a function approaches as the input approaches \(a\), independent of (and without requiring) the function's actual value at \(a\).
Question #2 Active Recall

For \(\lim_{x \to a} f(x)\) to exist, which condition must hold?

- **A)** \(f(a)\) must be defined
- **B)** \(f\) must be differentiable at \(a\)
- **C)** The left-hand limit \(\lim_{x \to a^-} f(x)\) and right-hand limit \(\lim_{x \to a^+} f(x)\) must both exist and be equal
- **D)** \(f\) must be a polynomial

Answer & Explanation:
**Answer: C)**

A two-sided limit exists precisely when both one-sided limits exist and agree; neither the function's value nor its differentiability at \(a\) is required.
Question #3 Active Recall

Evaluate \(\lim_{x \to 3} (x^2 - 5x + 6)\).

- **A)** \(-6\)
- **B)** \(0\)
- **C)** \(6\)
- **D)** \(3\)

Answer & Explanation:
**Answer: B)**

Since \(f(x) = x^2 - 5x + 6\) is a polynomial (continuous everywhere), the limit equals \(f(3) = 9 - 15 + 6 = 0\) by direct substitution.
Question #4 Active Recall

Evaluate \(\lim_{x \to 2} \dfrac{x^2 - 4}{x - 2}\).

- **A)** \(0\)
- **B)** The limit does not exist
- **C)** \(4\)
- **D)** \(2\)

Answer & Explanation:
**Answer: C)**

Factor the numerator: \(\dfrac{(x-2)(x+2)}{x-2} = x + 2\) for \(x \ne 2\). Taking the limit of the simplified expression gives \(2 + 2 = 4\); the original \(0/0\) form is resolved by canceling the common factor.
Question #5 Active Recall

Evaluate \(\lim_{x \to 0} \dfrac{\sqrt{x+4} - 2}{x}\).

- **A)** \(\dfrac{1}{4}\)
- **B)** \(0\)
- **C)** \(4\)
- **D)** The limit does not exist

Answer & Explanation:
**Answer: A)**

Multiply by the conjugate: \(\dfrac{(\sqrt{x+4}-2)(\sqrt{x+4}+2)}{x(\sqrt{x+4}+2)} = \dfrac{x}{x(\sqrt{x+4}+2)} = \dfrac{1}{\sqrt{x+4}+2}\). As \(x \to 0\), this approaches \(\dfrac{1}{2+2} = \dfrac{1}{4}\).
Question #6 Active Recall

Which limit law justifies \(\lim_{x \to a} [f(x) \cdot g(x)] = \lim_{x \to a} f(x) \cdot \lim_{x \to a} g(x)\)?

- **A)** The Squeeze Theorem
- **B)** The Product Law for limits, valid when both individual limits exist
- **C)** The Intermediate Value Theorem
- **D)** L'Hopital's Rule

Answer & Explanation:
**Answer: B)**

The Product Law states that the limit of a product equals the product of the limits, provided each individual limit exists.
Question #7 Active Recall

\(\lim_{x \to 1} \dfrac{x^2 - 1}{x - 1}\) is an example of which indeterminate form before simplification?

- **A)** \(\infty - \infty\)
- **B)** \(1^\infty\)
- **C)** \(0/0\)
- **D)** \(\infty/\infty\)

Answer & Explanation:
**Answer: C)**

Direct substitution of \(x=1\) gives \(\dfrac{1-1}{1-1} = \dfrac{0}{0}\), an indeterminate form that requires algebraic manipulation (here, factoring) before the limit can be evaluated.
Question #8 Active Recall

The Squeeze Theorem states that if \(g(x) \le f(x) \le h(x)\) near \(a\) (except possibly at \(a\)) and \(\lim_{x \to a} g(x) = \lim_{x \to a} h(x) = L\), then what can be concluded?

- **A)** \(f\) is continuous at \(a\)
- **B)** \(\lim_{x \to a} f(x) = L\) as well
- **C)** \(f(a) = L\)
- **D)** No conclusion can be drawn about \(f\)

Answer & Explanation:
**Answer: B)**

Being trapped between two functions with the same limit forces \(f\) to share that limit -- this is exactly the Squeeze (Sandwich) Theorem's conclusion.

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