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Calculus I: Infinite Limits and Vertical Asymptotes

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Chapter 2: Limits

Infinite Limits

Infinite limits describe the behavior of a function as its values increase or decrease without bound near a particular point. This concept is essential for understanding discontinuities and asymptotic behavior in calculus.

  • Definition: If f(x) grows arbitrarily large for all x sufficiently close (but not equal) to a, we write: and say the limit of f(x) as x approaches a is infinity.

  • Negative Infinite Limit: If f(x) is negative and grows arbitrarily large in magnitude for all x sufficiently close (but not equal) to a, we write: and say the limit of f(x) as x approaches a is negative infinity.

  • Non-existence: In both cases, the limit does not exist in the traditional sense, but describes unbounded behavior.

Graph illustrating an infinite limit where f(x) approaches negative infinity as x approaches a

One-Sided Infinite Limits

One-sided infinite limits consider the behavior of a function as x approaches a value from only one side (left or right).

  • Right-Sided Infinite Limit: If f(x) becomes arbitrarily large for all x sufficiently close to a with x > a, we write:

  • Left-Sided Infinite Limit: Analogously, for x < a:

  • Negative infinite limits are written similarly, replacing with .

Vertical Asymptotes

A vertical asymptote occurs at x = a if the function increases or decreases without bound as x approaches a from either side.

  • Definition: If , , or , then the line x = a is a vertical asymptote of f.

Examples and Applications

Example: Evaluating Infinite Limits

  • Example 1:

  • Example 2:

Example: One-Sided Infinite Limits

  • is undefined (since the left and right limits are not equal).

Graph of g(x) with vertical asymptotes at x=2 and x=4, used to analyze one-sided and two-sided limits

Example: Determining Limits Analytically

  • Example 3:

  • Example 4:

  • Example 5:

  • Example 6:

  • Example 7:

  • Example 8:

Example: Location of Vertical Asymptotes

Let . Find the vertical asymptotes and evaluate the following limits:

Vertical asymptotes occur where the denominator is zero and the numerator is not zero, i.e., at and .

Summary Table: Infinite Limits and Vertical Asymptotes

Type of Limit

Symbolic Form

Behavior

Infinite Limit

f(x) increases without bound as x approaches a

Negative Infinite Limit

f(x) decreases without bound as x approaches a

Right-Sided Infinite Limit

f(x) increases without bound as x approaches a from the right

Left-Sided Infinite Limit

f(x) increases without bound as x approaches a from the left

Vertical Asymptote

x = a

Occurs if any one-sided or two-sided limit is infinite at x = a

Additional info: The above notes expand on the definitions and examples provided in the slides, adding context and a summary table for clarity. The images included directly illustrate infinite limits and vertical asymptotes as discussed in the text.

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