DP IB Maths: AA HL

Topic Questions

5.7 Basic Limits & Continuity

1a
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2 marks

For each of the following, either show that the limit converges and find its value, or else explain why the limit diverges:

limit as x rightwards arrow 2 over 5 offraction numerator 1 over denominator 4 x squared minus 25 end fraction
1b
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2 marks

limit as x rightwards arrow 5 over 2 offraction numerator 1 over denominator 4 x squared minus 25 end fraction

1c
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3 marks

limit as x rightwards arrow 5 over 2 offraction numerator 2 x minus 5 over denominator 4 x squared minus 25 end fraction

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2a
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3 marks

Evaluate the limit

 limit as x rightwards arrow negative infinity of open parentheses fraction numerator 5 plus open parentheses 2 x minus 3 close parentheses squared over denominator 2 x squared end fraction close parentheses 

justifying your answer by clear mathematical reasoning.

2b
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4 marks
(i)

Show that the limit

 limit as x rightwards arrow plus infinity of fraction numerator x squared minus x plus 3 over denominator x end fraction

   diverges.  Be sure to show clear algebraic working.

(ii)
Determine any asymptotes on the graph of the curve with equation  
       

 y equals fraction numerator x squared minus x plus 3 over denominator x end fraction

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3a
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2 marks

A student has attempted to evaluate the limit

limit as x rightwards arrow plus infinity of open parentheses fraction numerator x squared plus x over denominator x cubed end fraction close parentheses

as follows:

limit as x rightwards arrow plus infinity of open parentheses fraction numerator x squared plus x over denominator x cubed end fraction close parentheses equals fraction numerator open parentheses plus infinity close parentheses squared plus open parentheses plus infinity close parentheses over denominator open parentheses plus infinity close parentheses cubed end fraction equals fraction numerator plus infinity over denominator plus infinity end fraction equals 1

Explain what is wrong with the student’s work.

3b
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2 marks

Determine the correct evaluation of the limit, justifying your answer by clear mathematical reasoning.

3c
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2 marks

Use technology to help you sketch the graph of y equals fraction numerator x squared plus x over denominator x cubed end fraction, and show that the graph confirms your answer to part (b).

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4a
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3 marks

Consider the function f defined by

f left parenthesis x right parenthesis equals 1 over open parentheses 2 x plus 6 close parentheses squared 

Evaluate the limits

(i)
limit as x rightwards arrow negative 3 to the power of minus of f left parenthesis x right parenthesis
(ii)
limit as x rightwards arrow negative 3 to the power of plus of f left parenthesis x right parenthesis
4b
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3 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of f left parenthesis x right parenthesis
(ii)
limit as x rightwards arrow plus infinity of f left parenthesis x right parenthesis
4c
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2 marks

Use your results from parts (a) and (b) to write down the equations of any asymptotes on the graph of y equals f left parenthesis x right parenthesis.

4d
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2 marks

Use technology to help you sketch the graph of y equals f left parenthesis x right parenthesis,  and show that this confirms your results from parts (a), (b) and (c).

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5a
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3 marks

Consider the function g defined by

 g left parenthesis x right parenthesis equals fraction numerator 1 over denominator x cubed minus 8 end fraction plus 1

Evaluate the limits

(i)
limit as x rightwards arrow 2 to the power of minus of g open parentheses x close parentheses
(ii)
limit as x rightwards arrow 2 to the power of plus of g open parentheses x close parentheses
5b
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3 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of g left parenthesis x right parenthesis
(ii)
limit as x rightwards arrow plus infinity of g left parenthesis x right parenthesis
5c
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2 marks

Use your results from parts (a) and (b) to write down the equations of any asymptotes on the graph of y equals g open parentheses x close parentheses.

5d
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2 marks

Use technology to help you sketch the graph of y equals g open parentheses x close parentheses,  and show that this confirms your results from parts (a), (b) and (c).

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6a
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3 marks

The function f is a piecewise function defined by 

 f open parentheses x close parentheses equals open curly brackets table row cell 3 x minus 7 comma space space space space space end cell cell x less than 3 end cell row cell space space space space space space 1 comma end cell cell x equals 3 end cell row cell x squared minus 8 x plus 17 comma end cell cell x greater than 3 end cell end table close

Explain why f is not continuous at x equals 3.

6b
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3 marks

Give an example of a function g that is continuous for all values of x element of straight real numbers, but is not differentiable for all values of x element of straight real numbers.  Include a sketch of the graph of the function, identifying the point(s) where the function is not differentiable.

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1a
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2 marks

For each of the following, either show that the limit converges and find its value, or else explain why the limit diverges:

limit as x rightwards arrow 4 of blank fraction numerator 1 over denominator x squared minus 9 end fraction 
1b
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2 marks

limit as x rightwards arrow 3 of blank fraction numerator 1 over denominator x squared minus 9 end fraction

1c
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3 marks

limit as x rightwards arrow 3 of blank fraction numerator x minus 3 over denominator x squared minus 9 end fraction

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2a
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2 marks

Evaluate the limit 

limit as x rightwards arrow negative infinity of blank open parentheses 13 minus 619 over x squared close parentheses

justifying your answer by clear mathematical reasoning.

2b
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3 marks

Show that the limit 

limit as x rightwards arrow plus infinity of blank fraction numerator 3 x squared minus 5 x plus 7 over denominator x squared end fraction 

converges, and find its value.  Be sure to show clear algebraic working.

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3a
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2 marks

A student has attempted to evaluate the limit 

limit as x rightwards arrow plus infinity of blank open parentheses x cubed minus x close parentheses 

as follows: 

limit as x rightwards arrow plus infinity of open parentheses x cubed minus x close parentheses equals open parentheses plus infinity close parentheses cubed minus open parentheses plus infinity close parentheses equals open parentheses plus infinity close parentheses minus open parentheses plus infinity close parentheses equals 0 

Explain what is wrong with the student’s work.

3b
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2 marks

Determine the correct evaluation of the limit, justifying your answer by clear mathematical reasoning.

3c
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2 marks

Use technology to help you sketch the graph of y equals x cubed minus x, and show that the graph confirms your answer to part (b).

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4a
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3 marks

Consider the function  defined by

space f open parentheses x close parentheses equals 1 over x squared 

Evaluate the limits

(i)
limit as x rightwards arrow 0 to the power of minus of f open parentheses x close parentheses

(ii)
limit as x rightwards arrow 0 to the power of plus of f open parentheses x close parentheses

4b
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3 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of f open parentheses x close parentheses 

(ii)
limit as x rightwards arrow plus infinity of f open parentheses x close parentheses
4c
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2 marks

Use your results from parts (a) and (b) to write down the equations of any asymptotes on the graph of  y equals f left parenthesis x right parenthesis.

4d
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2 marks

Use technology to help you sketch the graph of y equals f left parenthesis x right parenthesis, and show that this confirms your results from parts (a), (b) and (c).

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5a
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3 marks

Consider the function g defined by 

g open parentheses x close parentheses equals fraction numerator 1 over denominator x minus 5 end fraction 

Evaluate the limits

(i)
limit as x rightwards arrow 5 to the power of minus of g open parentheses x close parentheses

(ii)
limit as x rightwards arrow 5 to the power of plus of g open parentheses x close parentheses
5b
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3 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of g open parentheses x close parentheses 

(ii)
limit as x rightwards arrow plus infinity of g open parentheses x close parentheses
5c
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2 marks

Use your results from parts (a) and (b) to write down the equations of any asymptotes on the graph of y equals g left parenthesis x right parenthesis.

5d
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2 marks

Use technology to help you sketch the graph of y equals g left parenthesis x right parenthesis, and show that this confirms your results from parts (a), (b) and (c).

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6a
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3 marks

The functionspace f is a piecewise function defined by

 space f open parentheses x close parentheses equals open curly brackets table row cell blank x squared blank comma blank x less or equal than 2 end cell row cell x plus 3 comma blank x greater than 2 end cell end table close 

Explain whyspace f is not continuous at x equals 2.

6b
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2 marks

A function g is defined for all x element of straight real numbers, and it is differentiable at all points x element of straight real numbers.

Explain why g is continuous at  x equals 7.

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1a
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2 marks

For each of the following, either show that the limit converges and find its value, or else explain why the limit diverges:

limit as x rightwards arrow 0 of tan open parentheses x minus straight pi over 4 close parentheses
1b
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2 marks

limit as x rightwards arrow fraction numerator 3 straight pi over denominator 4 end fraction of tan open parentheses x minus straight pi over 4 close parentheses

1c
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3 marks

limit as x rightwards arrow fraction numerator 3 straight pi over denominator 4 end fraction of fraction numerator tan open parentheses x minus pi over 4 close parentheses over denominator sec open parentheses x minus pi over 4 close parentheses end fraction

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2a
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3 marks

Evaluate the limit

 limit as x rightwards arrow plus infinity of cos open parentheses 3 over x squared close parentheses

justifying your answer by clear mathematical reasoning.

2b
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5 marks
(i)
Show that the limit

 limit as x rightwards arrow negative infinity of open parentheses fraction numerator 2 x cubed plus 6 x squared plus 1 over denominator 2 x squared end fraction plus tan open parentheses fraction numerator pi x cubed minus 2 x squared plus 3 over denominator 7 minus 2 x minus 4 x cubed end fraction close parentheses close parentheses 

diverges.  Be sure to show clear algebraic working.

 

(ii)
Determine the asymptotic behaviour of the curve with equation

 y equals fraction numerator 2 x cubed plus 6 x squared plus 1 over denominator 2 x squared end fraction plus tan open parentheses fraction numerator pi x cubed minus 2 x squared plus 3 over denominator 7 minus 2 x minus 4 x cubed end fraction close parentheses        

as x rightwards arrow plus-or-minus infinity.

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3a
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2 marks

A student has attempted to evaluate the limit

 limit as x rightwards arrow negative infinity of open parentheses fraction numerator x squared plus x plus 14 over denominator x squared plus x minus 2 end fraction close parentheses 

as follows:

limit as x rightwards arrow negative infinity of open parentheses fraction numerator x squared plus x plus 14 over denominator x squared plus x minus 2 end fraction close parentheses equals fraction numerator open parentheses negative infinity close parentheses squared plus open parentheses negative infinity close parentheses plus 14 over denominator open parentheses negative infinity close parentheses squared plus open parentheses negative infinity close parentheses minus 2 end fraction equals fraction numerator open parentheses plus infinity close parentheses plus open parentheses negative infinity close parentheses plus 14 over denominator open parentheses plus infinity close parentheses plus open parentheses negative infinity close parentheses minus 2 end fraction equals fraction numerator 0 plus 14 over denominator 0 minus 2 end fraction equals negative 7

 

Explain what is wrong with the student’s work.

3b
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2 marks

Determine the correct evaluation of the limit, justifying your answer by clear mathematical reasoning.

3c
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2 marks

Use technology to help you sketch the graph of y equals fraction numerator x squared minus x plus 14 over denominator x squared minus x minus 2 end fraction, and show that the graph confirms your answer to part (b).

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4a
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3 marks

Consider the function f defined by

f open parentheses x close parentheses equals 1 over open parentheses arctan space x close parentheses squared 

Evaluate the limits

(i)
limit as x rightwards arrow 0 to the power of minus of f open parentheses x close parentheses
(ii)
limit as x rightwards arrow 0 to the power of plus of f open parentheses x close parentheses

 

4b
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4 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of f open parentheses x close parentheses
(ii)
limit as x rightwards arrow plus infinity of f open parentheses x close parentheses
4c
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2 marks

Use your results from parts (a) and (b) to write down the equations of any asymptotes on the graph of y equals f open parentheses x close parentheses.

4d
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2 marks

Use technology to help you sketch the graph of y equals f open parentheses x close parentheses,  and show that this confirms your results from parts (a), (b) and (c).

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5a
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3 marks

Consider the function g defined by

 g open parentheses x close parentheses equals fraction numerator 2 x minus 3 over denominator x end fraction minus fraction numerator 1 over denominator x squared plus 1 end fraction

Evaluate the limits

(i)
limit as x rightwards arrow negative 1 to the power of minus of g open parentheses x close parentheses
(ii)
limit as x rightwards arrow negative 1 to the power of plus of g open parentheses x close parentheses
5b
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3 marks

Evaluate the limits

(i)
limit as x rightwards arrow negative infinity of g open parentheses x close parentheses
(ii)
limit as x rightwards arrow plus infinity of g open parentheses x close parentheses
5c
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3 marks

Write down the equations of any asymptotes on the graph of y equals g open parentheses x close parentheses.

5d
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2 marks

Use technology to help you sketch the graph of y equals g open parentheses x close parentheses,  and show that this confirms your results from parts (a), (b) and (c).

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6a
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3 marks

The function f is a piecewise function defined by

f open parentheses x close parentheses equals open curly brackets table row cell space space space space 10 minus 3 x comma space space space space space space space space space space end cell cell x less than 2 end cell row cell space space space space fraction numerator x squared minus 4 over denominator x minus 2 end fraction comma end cell cell x equals 2 end cell row cell open vertical bar x squared minus 2 x minus 4 close vertical bar comma end cell cell x greater than 2 end cell end table close

 Explain why f is not continuous at x equals 2.

6b
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3 marks

Give an example of a function g that is continuous for all x element of straight real numbers,  but which is not differentiable at  x equals 3.  Include a sketch of the graph of the function, identifying all points where the function is not differentiable.

6c
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2 marks

Write down a continuous function h for which limit as x rightwards arrow negative infinity of h open parentheses x close parentheses  and limit as x rightwards arrow plus infinity of h open parentheses x close parentheses  both exist and are finite, but for which limit as x rightwards arrow negative infinity of h open parentheses x close parentheses not equal to limit as x rightwards arrow plus infinity of h open parentheses x close parentheses.

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