Calculus 2 : Limits

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #161 : Limits

Evaluate the limit:

\(\displaystyle \lim_{x\rightarrow \pi^{+}}(-\tan(x))\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle \infty\)

\(\displaystyle 1\)

\(\displaystyle -1\)

Correct answer:

\(\displaystyle 0\)

Explanation:

When we evaluate the limit, we find that as \(\displaystyle tan(x)\) approaches \(\displaystyle \pi\), we approach \(\displaystyle 0\). Because there is a negative sign in front of the function (we were given \(\displaystyle -tan(x))\), the answer is still \(\displaystyle 0\).

The fact that the limit is right sided doesn't change the outcome.

Example Question #115 : Finding Limits And One Sided Limits

Screen shot 2015 07 28 at 11.51.52 am

Given the above graph of \(\displaystyle f(x)\), what is \(\displaystyle \lim_{x\rightarrow 0^{+}}f(x)\)?

Possible Answers:

Does Not Exist

\(\displaystyle -\infty\)

\(\displaystyle 0\)

\(\displaystyle \infty\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle -\infty\)

Explanation:

We first need to determine what the question is asking for. In this case because there is a plus sign in the exponent of zero we can interpret that as the limit of the function as x values approach zero from the right hand side. This means the values are going to be slightly larger than zero.

Examining the graph, we can observe that \(\displaystyle \lim_{x\rightarrow 0^{+}}f(x)=-\infty\)  as \(\displaystyle x\)  approaches \(\displaystyle 0\) from the right.

Example Question #161 : Calculus Ii

Screen shot 2015 07 28 at 11.58.54 am

Given the above graph of \(\displaystyle f(x)\), what is \(\displaystyle \lim_{x\rightarrow 0}f(x)\)?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle -\infty\)

\(\displaystyle 1\)

Does Not Exist

\(\displaystyle -1\)

Correct answer:

\(\displaystyle -\infty\)

Explanation:

First we want to check the three conditions for which a function  is continuous at a point :

  1. A value  exists in the domain of 

  2. The limit of  exists as  approaches 

  3. The limit of  at  is equal to 

Given , we can see that condition #1 is satisfied because the graph is approaching negative infinity at .

We can also see that condition #2 is satisfied because  approaches  from the right and from the left.

Based on the above, condition #3 is also satisfied because  is equal to .

Thus by examining the graph, we can observe that \(\displaystyle \lim_{x\rightarrow 0}f(x)=-\infty\)  as \(\displaystyle x\)  approaches \(\displaystyle 0\) from the left and from the right.

Example Question #161 : Limits

Evaluate the limit:

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

Possible Answers:

\(\displaystyle -\frac{1}{3}\)

\(\displaystyle DNE\)

\(\displaystyle \infty\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle -\frac{1}{3}\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=-1; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation.

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

Example Question #121 : Finding Limits And One Sided Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to 2}\frac{x^2+5x-14}{x^2-5x+6}\)

Possible Answers:

\(\displaystyle \infty\)

\(\displaystyle -9\)

\(\displaystyle 0\)

\(\displaystyle DNE\)

Correct answer:

\(\displaystyle -9\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=2; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation.

\(\displaystyle \\ \lim_{x \to 2}\frac{x^2+5x-14}{x^2-5x+6}\\ \\=\lim_{x \to 2}\frac{(x-2)(x+7)}{(x-2)(x-3)}\\ \\=\lim_{x \to 2}\frac{x+7}{x-3}\\ \\=\frac{2+7}{2-3}\\ \\=\frac{9}{-1}\\ \\=-9\)

Example Question #122 : Finding Limits And One Sided Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to 3}\frac{x^2-6x+9}{x^4-81}\)

Possible Answers:

\(\displaystyle \infty\)

\(\displaystyle 0\)

\(\displaystyle -\infty\)

\(\displaystyle DNE\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=3; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation.

\(\displaystyle \\ \lim_{x \to 3}\frac{x^2-6x+9}{x^4-81}\\ \\=\lim_{x \to 3}\frac{(x-3)(x-3)}{(x^2+9)(x^2-9)}\\ \\=\lim_{x \to 3}\frac{(x-3)(x-3)}{(x^2+9)(x+3)(x-3)}\\ \\=\lim_{x \to 3}\frac{x-3}{(x^2+9)(x+3)}\\ \\=\frac{3-3}{(3^2+9)(3+3)}\\ \\=\frac{0}{(9+9)(6)}\\ \\=\frac{0}{18*6}\\ \\=\frac{0}{108}=0\)

Example Question #161 : Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to 9}\frac{x^2-9x}{x^2-8x-9}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle \infty\)

\(\displaystyle \frac{9}{10}\)

\(\displaystyle DNE\)

Correct answer:

\(\displaystyle \frac{9}{10}\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=9; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation.

\(\displaystyle \\\lim_{x \to 9}\frac{x^2-9x}{x^2-8x-9}\\ \\=\lim_{x \to 9}\frac{x(x-9)}{(x-9)(x+1)}\\ \\=\lim_{x \to 9}\frac{x}{x+1}\\ \\=\frac{9}{9+1}=\frac{9}{10}\)

Example Question #124 : Finding Limits And One Sided Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to -3}\frac{x^2-9}{x^2+7x+12}\)

Possible Answers:

\(\displaystyle -6\)

\(\displaystyle 0\)

\(\displaystyle DNE\)

\(\displaystyle \infty\)

Correct answer:

\(\displaystyle -6\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=-3; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation.

\(\displaystyle \\\lim_{x \to -3}\frac{x^2-9}{x^2+7x+12}\\ \\=\lim_{x \to -3}\frac{(x+3)(x-3)}{(x+3)(x+4)}\\ \\=\lim_{x \to -3}\frac{x-3}{x+4}\\ \\=\frac{-3-3}{-3+4}\\ \\=\frac{-6}{1}\\ \\=-6\)

Example Question #122 : Finding Limits And One Sided Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to 0}\frac{x^3+x^2}{x^4+x^3}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle \infty\)

\(\displaystyle -\infty\)

\(\displaystyle DNE\)

Correct answer:

\(\displaystyle DNE\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will equal zero when x=0; so we try to eliminate the denominator by factoring.

When the denominator is no longer zero, we may continue to insert the value of x into the remaining equation. We see that we can no longer factor this to make the denominator not equal 0; hence this limit DNE because the denominator is zero.

\(\displaystyle \\ \lim_{x \to 0}\frac{x^3+x^2}{x^4+x^3}\\ \\=\lim_{x \to 0}\frac{x^2(x+1)}{x^3(x+1)}\\ \\=\lim_{x \to 0}\frac{1}{x}\\ \\=\frac{1}{0}\Rightarrow DNE\)

Example Question #162 : Limits

Evaluate the limit:

\(\displaystyle \lim_{x \to 2}\frac{x-2}{x+2}\)

Possible Answers:

\(\displaystyle -\infty\)

\(\displaystyle 0\)

\(\displaystyle \infty\)

\(\displaystyle DNE\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The limiting situation in this equation would be the denominator. Plug the value that x is approaching into the denominator to see if the denominator will equal 0. In this question, the denominator will not equal zero when x=2; so we proceed to insert the value of x into the entire equation.

\(\displaystyle \lim_{x \to 2}\frac{x-2}{x+2}=\frac{2-2}{2+2}=\frac{0}{4}=0\)

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