Mathematics
Grade 12
15 min
Find the limit at a vertical asymptote of a rational function II
Find the limit at a vertical asymptote of a rational function II
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1
Introduction & Learning Objectives
Learning Objectives
Determine the one-sided limits (from the left and right) of a rational function at a vertical asymptote.
Analyze the signs of the numerator and denominator as x approaches a vertical asymptote from each side.
Conclude whether the limit at a vertical asymptote is positive infinity, negative infinity, or does not exist.
Differentiate between vertical asymptotes and removable discontinuities by analyzing common factors.
Evaluate limits at vertical asymptotes where the denominator has a factor raised to an even or odd power.
Apply the concept of one-sided limits to sketch the behavior of a rational function's graph near its vertical asymptotes.
What happens when you divide by a number that's almost zero? Does it matter if it's a tiny positive o...
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Key Concepts & Vocabulary
TermDefinitionExample
Vertical Asymptote (VA)A vertical line x = c where the function f(x) approaches positive or negative infinity as x approaches c from the left or right. It occurs where the denominator of a simplified rational function is zero.The function f(x) = 1/(x-2) has a vertical asymptote at x=2.
One-Sided LimitThe value a function approaches as x approaches a point from only one side. It is denoted as lim x→c⁻ f(x) (from the left) and lim x→c⁺ f(x) (from the right).For f(x) = 1/x, the limit as x approaches 0 from the right is lim x→0⁺ (1/x) = ∞.
Infinite LimitA limit in which the function's value increases or decreases without bound as x approaches a certain number. The result is written as ∞ or -∞.The limit of f(x) = 1/x² as x approaches 0 is ∞.
Sign AnalysisThe process...
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Core Formulas
One-Sided Limit Sign Analysis
To find \lim_{x \to c^+} f(x) or \lim_{x \to c^-} f(x): \newline 1. Determine the sign of the Numerator as x → c. \newline 2. Determine the sign of the Denominator as x approaches c from the specified side. \newline 3. Use sign rules: \frac{(+)}{(+)} \to +\infty, \frac{(+)}{(-)} \to -\infty, \frac{(-)}{(+)} \to -\infty, \frac{(-)}{(-)} \to +\infty.
This is the primary method for determining the behavior at a vertical asymptote. Use a test value very close to 'c' on the appropriate side (e.g., c+0.1 for c⁺, c-0.1 for c⁻) to find the signs.
Even/Odd Power Rule at Asymptotes
Consider the factor (x-c)^n in the simplified denominator that causes the asymptote. \newline If n is even, \lim_{x \to c^-} f(x) = \lim_{x \to c^+} f(x). (Behavior is...
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Challenging
A rational function g(x) has a single vertical asymptote at x=-4. It is known that lim x→-4 g(x) = +∞. Which of the following could be the simplified form of g(x)?
A.g(x) = 1/(x+4)
B.g(x) = 1/(x+4)²
C.g(x) = -1/(x+4)
D.g(x) = -1/(x+4)²
Challenging
Evaluate the limit: lim x→2⁺ (x-3)/((x-2)⁵)
A.-∞
B.+∞
C.0
D.Does not exist
Challenging
For a simplified rational function f(x) with a vertical asymptote at x=c caused by a denominator factor of (x-c)ⁿ, if we know that lim x→c⁻ f(x) and lim x→c⁺ f(x) are finite and equal, what must be true?
A.n must be a large even integer.
B.n must be a large odd integer.
C.The numerator must also have a factor of (x-c)ⁿ.
D.This scenario is impossible; the limits at a vertical asymptote cannot be finite.
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