Calculus 2 : Limits

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #171 : Calculus Ii

Evaluate the limit:

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

Possible Answers:

\displaystyle -\infty

\displaystyle DNE

\displaystyle 0

\displaystyle \infty

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

Example Question #129 : Finding Limits And One Sided Limits

Screen shot 2015 07 27 at 12.31.44 pm

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

Possible Answers:

Does Not Exist

\displaystyle 1

\displaystyle \infty

\displaystyle -\infty

\displaystyle -1

Correct answer:

Does Not Exist

Explanation:

Examining the graph, we can observe that does not exist, as   is not continuous at . We can see this by checking 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 not satisfied because the graph has a vertical asymptote instead of only one value for and is therefore an infinite discontinuity at .

We can also see that condition #2 is not satisfied because approaches two different limits: \displaystyle -\infty  from the left and \displaystyle \infty from the right.

Based on the above, condition #3 is also not satisfied because is not equal to the multiple values of .

Thus, does not exist.

Example Question #130 : Finding Limits And One Sided Limits

Screen shot 2015 07 28 at 6.24.36 pm

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

Possible Answers:

\displaystyle 0

\displaystyle -\infty

\displaystyle \infty

Does Not Exist

\displaystyle 1

Correct answer:

Does Not Exist

Explanation:

Examining the graph, we can observe that does not exist, as   is not continuous at . We can see this by checking 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 not satisfied because the graph has a vertical asymptote instead of only one value for and is therefore an infinite discontinuity at .

We can also see that condition #2 is not satisfied because approaches two different limits:  from the left and from the right.

Based on the above, condition #3 is also not satisfied because is not equal to the multiple values of .

Thus, does not exist.

 

 

Example Question #171 : Calculus Ii

Screen shot 2015 07 29 at 1.21.58 pm

Given the above graph of \displaystyle f(x), what is \displaystyle \lim_{x\rightarrow 5}f(x)?

Possible Answers:

\displaystyle 5

Does Not Exist

\displaystyle -\infty

\displaystyle 0

\displaystyle \infty

Correct answer:

Does Not Exist

Explanation:

Examining the graph, we can observe that \displaystyle \lim_{x\rightarrow 5}f(x) does not exist, as   is not continuous at \displaystyle x=5. We can see this by checking 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 \displaystyle c=5, we can see that condition #1 is not satisfied because the graph has a vertical asymptote instead of only one value for \displaystyle f(5) and is therefore an infinite discontinuity at \displaystyle (5,f(5)).

We can also see that condition #2 is not satisfied because \displaystyle \lim_{x\rightarrow 5}f(x) approaches two different limits: \displaystyle -\infty  from the left and \displaystyle \infty from the right.

Based on the above, condition #3 is also not satisfied because \displaystyle \lim_{x\rightarrow 5}f(x) is not equal to the multiple values of .

Thus, \displaystyle \lim_{x\rightarrow 5}f(x) does not exist.

Example Question #172 : Calculus Ii

Screen shot 2015 07 27 at 11.18.59 am

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

Possible Answers:

\displaystyle 1

\displaystyle -\infty

\displaystyle -1

\displaystyle 0

\displaystyle \infty

Correct answer:

\displaystyle -\infty

Explanation:

Examining the graph above, we need to look at three things:

1) What is the limit of the function as \displaystyle x approaches zero from the left?

2) What is the limit of the function as \displaystyle x approaches zero from the right?

3) What is the function value as \displaystyle x=0 and is it the same as the result from statement one and two?

Thus, 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 #173 : Calculus Ii

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

Possible Answers:

\displaystyle 0

\displaystyle \infty

\displaystyle -\infty

\displaystyle 1

\displaystyle -1

Correct answer:

\displaystyle \infty

Explanation:

First we need to determine if this is a left or right sided limit. Since there is a plus sign in the exponent on the zero that means it is a right sided limit. This means we want to look at the function values for x values that are slightly larger than zero.

Therefore 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 #174 : Calculus Ii

Screen shot 2015 07 28 at 6.08.19 pm

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 1

\displaystyle 0

\displaystyle \infty

Correct answer:

\displaystyle \infty

Explanation:

Examining the graph, we want to find where the graph tends to as it approaches zero from the left hand side. We can see that there appears to be a vertical asymptote at zero. As the x values approach zero from the left, the function values of the graph tend towards positive infinity.

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

Example Question #175 : Calculus Ii

Screen shot 2015 07 28 at 6.16.14 pm

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

Possible Answers:

\displaystyle 1

\displaystyle \infty

\displaystyle -\infty

\displaystyle -1

Does Not Exist

Correct answer:

\displaystyle \infty

Explanation:

First we need to determine what the question is asking. Since there is a plus sign in the exponent on the zero this indicates that we are looking for a right sided limit. This means we want to look at the function values for values 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 #176 : Calculus Ii

Screen shot 2015 07 29 at 1.10.20 pm

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

Possible Answers:

\displaystyle -\infty

\displaystyle \infty

\displaystyle -1

\displaystyle 0

\displaystyle 1

Correct answer:

\displaystyle \infty

Explanation:

Examining the graph, we want to find where the graph tends to as it approaches zero from the left hand side. We can see that there appears to be a vertical asymptote at zero. As the x values approach zero from the left, the function values of the graph tend towards positive infinity.

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

Example Question #177 : Calculus Ii

Screen shot 2015 07 29 at 1.16.48 pm

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

Possible Answers:

Does Not Exist

\displaystyle 1

\displaystyle -1

\displaystyle \infty

\displaystyle -\infty

Correct answer:

\displaystyle \infty

Explanation:

Examining the graph, we want to find where the graph tends to as it approaches zero from the right hand side. We can see that there appears to be a vertical asymptote at zero. As the x values approach zero from the right, the function values of the graph tend towards positive infinity.

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

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