Calculus I · Limits and Continuity · practice

Infinite Limits and Asymptote Practice

Visual study stop

Read the picture before the symbols

Pause at each graph long enough to say what the input is doing, what the output is doing, and which feature supports the next mathematical decision.

Two panels comparing odd and even reciprocal powers near x = 1.
Read this graph as text

Odd and even powers at a vertical asymptote. Two ordered panels share the vertical asymptote x = 1. In the odd-power panel, y = 1/(x - 1) falls without bound from the left and rises without bound from the right. In the even-power panel, y = 1/(x - 1) squared rises without bound from both sides. Each panel uses explicit left and right domains and a dashed asymptote.

The odd-power curves are solid, the even-power curves are double-stroked, and both panels mark x = 1 with a dashed line and title.

Why it matters: Compare one-sided signs for reciprocal functions with odd and even denominator powers.

Read local blow-up one side at a time

Compare odd and even denominator powers before calculating. The parity determines whether the sign changes across the excluded input or remains the same on both sides.

Rational function approaching the horizontal asymptote y = 3 at both ends.
Read this graph as text

Approaching a horizontal asymptote. The rational curve f(x) = (3x squared - 2x + 5)/(x squared + 4) is drawn from x = -12 to x = 12. Its denominator never vanishes for real x. A dashed horizontal line marks y = 3, and both ends of the solid curve move closer to that line, showing equal limits at positive and negative infinity.

The function is a heavy solid curve and the asymptote is a dashed line labeled y = 3.

Why it matters: Connect equal-degree rational end behavior to the ratio of leading coefficients.

Then switch from local behavior to end behavior

At infinity, the graph is not approaching a finite input. Follow the long-run trend and use dominant terms to identify the horizontal level the outputs settle toward.

Section 4 Exercises

A. One-sided infinite limits

Exercise 1

limx41x4\displaystyle\lim_{x\to4^-}\frac1{x-4}

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-\infty.

Answer 1 from the source-traced unit appendix.
Exercise 2

limx4+1x4\displaystyle\lim_{x\to4^+}\frac1{x-4}

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++\infty.

Answer 2 from the source-traced unit appendix.
Exercise 3

limx01x2\displaystyle\lim_{x\to0^-}\frac1{x^2}

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++\infty.

Answer 3 from the source-traced unit appendix.
Exercise 4

limx0+1x3\displaystyle\lim_{x\to0^+}\frac1{x^3}

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++\infty.

Answer 4 from the source-traced unit appendix.
Exercise 5

limx2+x1x+2\displaystyle\lim_{x\to-2^+}\frac{x-1}{x+2}

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-\infty.

Answer 5 from the source-traced unit appendix.
Exercise 6

limx1x+3(x1)2\displaystyle\lim_{x\to1^-}\frac{x+3}{(x-1)^2}

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++\infty.

Answer 6 from the source-traced unit appendix.
Exercise 7

limx3x+2(x3)(x+1)\displaystyle\lim_{x\to3^-}\frac{x+2}{(x-3)(x+1)}

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-\infty.

Answer 7 from the source-traced unit appendix.
Exercise 8

limx3+x+2(x3)(x+1)\displaystyle\lim_{x\to3^+}\frac{x+2}{(x-3)(x+1)}

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++\infty.

Answer 8 from the source-traced unit appendix.
Exercise 9

limx12x(x+1)3\displaystyle\lim_{x\to-1^-}\frac{2-x}{(x+1)^3}

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-\infty.

Answer 9 from the source-traced unit appendix.
Exercise 10

limx1+2x(x+1)3\displaystyle\lim_{x\to-1^+}\frac{2-x}{(x+1)^3}

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++\infty.

Answer 10 from the source-traced unit appendix.

B. Holes and vertical asymptotes

Exercise 11

Find and classify discontinuities of x2(x2)(x+1)\dfrac{x-2}{(x-2)(x+1)}.

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Hole at 22; vertical asymptote at 1-1.

Answer 11 from the source-traced unit appendix.
Exercise 12

Find and classify discontinuities of x29(x3)(x+2)\dfrac{x^2-9}{(x-3)(x+2)}.

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Hole at 33; vertical asymptote at 2-2.

Answer 12 from the source-traced unit appendix.
Exercise 13

Find all holes and vertical asymptotes of (x+1)(x4)(x+1)(x2)2\dfrac{(x+1)(x-4)}{(x+1)(x-2)^2}.

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Hole at 1-1; vertical asymptote at 22.

Answer 13 from the source-traced unit appendix.
Exercise 14

Determine one-sided behavior at every vertical asymptote of x+3(x1)(x+2)\dfrac{x+3}{(x-1)(x+2)}.

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At x=1x=1: left -\infty, right ++\infty. At x=2x=-2: left ++\infty, right -\infty.

Answer 14 from the source-traced unit appendix.
Exercise 15

Determine one-sided behavior at every vertical asymptote of x5(x+1)2\dfrac{x-5}{(x+1)^2}.

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Both one-sided limits at 1-1 are -\infty.

Answer 15 from the source-traced unit appendix.
Exercise 16

Explain why a cancelled denominator factor creates a hole rather than a vertical asymptote.

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Cancellation removes the zero factor for nearby inputs, leaving a finite limiting value.

Answer 16 from the source-traced unit appendix.

C. Rational limits at infinity

Exercise 17

limx4x+1x2+7\displaystyle\lim_{x\to\infty}\frac{4x+1}{x^2+7}

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00.

Answer 17 from the source-traced unit appendix.
Exercise 18

limx2x235x2+x\displaystyle\lim_{x\to-\infty}\frac{2x^2-3}{5x^2+x}

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2/52/5.

Answer 18 from the source-traced unit appendix.
Exercise 19

limx7x3+x2x35\displaystyle\lim_{x\to\infty}\frac{7x^3+x}{2x^3-5}

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7/27/2.

Answer 19 from the source-traced unit appendix.
Exercise 20

limx3x4xx4+9\displaystyle\lim_{x\to-\infty}\frac{3x^4-x}{x^4+9}

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33.

Answer 20 from the source-traced unit appendix.
Exercise 21

limxx2+1x3+2\displaystyle\lim_{x\to\infty}\frac{x^2+1}{x^3+2}

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00.

Answer 21 from the source-traced unit appendix.
Exercise 22

limx5x3+1x24\displaystyle\lim_{x\to-\infty}\frac{5x^3+1}{x^2-4}

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-\infty.

Answer 22 from the source-traced unit appendix.
Exercise 23

limx2x5+xx5+3\displaystyle\lim_{x\to\infty}\frac{-2x^5+x}{x^5+3}

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2-2.

Answer 23 from the source-traced unit appendix.
Exercise 24

Find all horizontal asymptotes of 3x2+1x25x\dfrac{3x^2+1}{x^2-5x}.

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Horizontal asymptote y=3y=3.

Answer 24 from the source-traced unit appendix.
Exercise 25

Find the slant asymptote of x2+3x2\dfrac{x^2+3}{x-2}.

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Slant asymptote y=x+2y=x+2.

Answer 25 from the source-traced unit appendix.
Exercise 26

Use division to describe the end behavior of 2x3+xx21\dfrac{2x^3+x}{x^2-1}.

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Polynomial asymptote y=2xy=2x.

Answer 26 from the source-traced unit appendix.

D. Radicals at infinity

Exercise 27

limxx2+4x\displaystyle\lim_{x\to\infty}\frac{\sqrt{x^2+4}}{x}

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11.

Answer 27 from the source-traced unit appendix.
Exercise 28

limxx2+4x\displaystyle\lim_{x\to-\infty}\frac{\sqrt{x^2+4}}{x}

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1-1.

Answer 28 from the source-traced unit appendix.
Exercise 29

limx9x2+1x\displaystyle\lim_{x\to\infty}\frac{\sqrt{9x^2+1}}{x}

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33.

Answer 29 from the source-traced unit appendix.
Exercise 30

limx9x2+1x\displaystyle\lim_{x\to-\infty}\frac{\sqrt{9x^2+1}}{x}

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3-3.

Answer 30 from the source-traced unit appendix.
Exercise 31

limx(x2+8xx)\displaystyle\lim_{x\to\infty}\left(\sqrt{x^2+8x}-x\right)

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44.

Answer 31 from the source-traced unit appendix.
Exercise 32

limx(4x2+x2x)\displaystyle\lim_{x\to\infty}\left(\sqrt{4x^2+x}-2x\right)

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1/41/4.

Answer 32 from the source-traced unit appendix.
Exercise 33

limx(x2+6x+x)\displaystyle\lim_{x\to-\infty}\left(\sqrt{x^2+6x}+x\right)

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3-3.

Answer 33 from the source-traced unit appendix.
Exercise 34

Explain the exact point where x|x| must be used in a radical-at-infinity problem.

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Use x2=x\sqrt{x^2}=|x|; at negative infinity x=x|x|=-x.

Answer 34 from the source-traced unit appendix.

E. Mixed exam practice

Exercise 35

Analyze all discontinuities and asymptotes of x21x23x+2\dfrac{x^2-1}{x^2-3x+2}.

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Hole at 11, vertical asymptote x=2x=2, horizontal asymptote y=1y=1; one-sided limits at 22: ,+-\infty,+\infty.

Answer 35 from the source-traced unit appendix.
Exercise 36

Analyze all discontinuities and asymptotes of x24x2x2\dfrac{x^2-4}{x^2-x-2}.

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Hole at 22, vertical asymptote x=1x=-1, horizontal asymptote y=1y=1; one-sided limits at 1-1: ,+-\infty,+\infty.

Answer 36 from the source-traced unit appendix.
Exercise 37

Find the exact one-sided limits at every vertical asymptote of xx29\dfrac{x}{x^2-9}.

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At 3-3: left -\infty, right ++\infty. At 33: left -\infty, right ++\infty.

Answer 37 from the source-traced unit appendix.
Exercise 38

Find the end behavior of 2x3x+1x2+4\dfrac{2x^3-x+1}{x^2+4}, including any polynomial asymptote.

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Polynomial asymptote y=2xy=2x.

Answer 38 from the source-traced unit appendix.
Exercise 39

Construct a rational function with a hole at x=1x=1, a vertical asymptote at x=2x=-2, and horizontal asymptote y=3y=3.

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Example: (x1)(3x+1)(x1)(x+2)\dfrac{(x-1)(3x+1)}{(x-1)(x+2)}.

Answer 39 from the source-traced unit appendix.
Exercise 40

Explain why a graph may cross a horizontal asymptote but cannot take a finite value on a vertical asymptote where its formula is undefined.

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Horizontal asymptotes describe end behavior and may be crossed; a vertical asymptote occurs at an excluded finite input where the function is unbounded.

Answer 40 from the source-traced unit appendix.

Answers begin in the referenced section.

After the explanation

Use the section idea

Reading lens

Is the function growing without bound near a finite input, or settling into end behavior as the input grows?

Mental model

Vertical asymptotes describe local blow-up near an excluded finite input; end-behavior asymptotes describe the long-run trend as inputs grow in magnitude.

Decision

Near a denominator zero, build a sign chart for each side; at infinity, compare dominant powers or divide to expose the lasting term.

Common trap

Do not merge positive and negative infinity, and remember that square roots produce absolute values when factoring a large squared input.

Check yourself

You understand the section when you can predict signs and asymptotes before doing detailed algebra, then verify them with the expression.

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Vocab
Limit
Math glossaryLimit
limxaf(x)=L\lim_{x\to a}f(x)=L

The value a function approaches as its input approaches a target.

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Function
Math glossaryFunction
y=f(x)y=f(x)

A rule or relation assigning exactly one output to each allowed input.

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Continuity
Math glossaryContinuity
limxaf(x)=f(a)\lim_{x\to a}f(x)=f(a)

At a point, the function value exists and equals the limit there.

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Domain
Math glossaryDomain
domf\operatorname{dom}f

The set of permitted input values.

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Math glossary