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Practice Questions

1. Limits and Continuity

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Question 1

Graphing calculator required

The temperature inside an industrial oven is modelled by

T(t)=180145e0.11t10e0.50tT(t)=180-145e^{-0.11t}-10e^{-0.50t},

where T(t)T(t) is measured in degrees Celsius and t0t\geq0 is measured in minutes. The graph of TT is shown. Unless otherwise stated, round numerical answers to three decimal places.

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Part (a)(i)
[1]

Write an expression for the limiting temperature by evaluating limtT(t)\displaystyle\lim_{t\to\infty}T(t).

Part (a)(ii)
[1]

Interpret this limit in the context of the oven.

Part (b)
[2]

Calculate the first time at which the oven temperature reaches 150C150^\circ\mathrm{C}. Show the equation solved.

Part (c)
[2]

Calculate the average rate of change of the temperature from t=10t=10 to t=20t=20. Include units.

Part (d)
[2]

Determine whether the oven temperature at t=30t=30 is within 2C2^\circ\mathrm{C} of its limiting temperature. Justify your answer with a calculation.

Part (e)
[1]

Estimate the earliest time after which the temperature remains above 170C170^\circ\mathrm{C}.

Question 2

Graphing calculator not permitted

The graph of ff is shown. What is the value of

limx1f(x)+limx1+f(x)f(1)\displaystyle\lim_{x\to1^-}f(x)+\lim_{x\to1^+}f(x)-f(1)?

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A. 55

B. 66

C. 77

D. The expression does not exist.

[1]
Select Answer

Question 3

Graphing calculator required

The functions

f(x)=2+0.45x+0.55sin(1.3x)f(x)=2+0.45x+0.55\sin(1.3x)

and

g(x)=1.4+0.08(x1)2g(x)=1.4+0.08(x-1)^2

are continuous on [4,5][-4,5]. Their graphs are shown. For a number cc satisfying 4<c<5-4<c<5, define

hc(x)={f(x),x<c,\g(x),xc.h_c(x)=\begin{cases}f(x),&x<c,\g(x),&x\geq c.\end{cases}

Round calculator results to three decimal places.

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Part (a)(i)
[2]

Represent limxchc(x)\displaystyle\lim_{x\to c^-}h_c(x) and limxc+hc(x)\displaystyle\lim_{x\to c^+}h_c(x) in terms of f(c)f(c) and g(c)g(c).

Part (a)(ii)
[1]

Determine the condition that must be satisfied for hch_c to be continuous at x=cx=c.

Part (b)
[3]

Calculate all values of cc in (4,5)(-4,5) for which hch_c is continuous. Show the equation solved.

Part (c)
[2]

For c=2.5c=2.5, determine whether limxchc(x)\displaystyle\lim_{x\to c}h_c(x) exists. Justify your answer numerically.

Part (d)
[1]

Explain why every solution obtained in part (b) produces continuity at x=cx=c, rather than merely equal one-sided estimates from the displayed graph.

Question 4

GRAPHING CALCULATOR NOT PERMITTED

Let f(x)=x29x3f(x)=\dfrac{x^2-9}{x-3} for x3x\ne3. What is limx3f(x)\displaystyle\lim_{x\to3}f(x)?

A. 00

B. 66

C. 33

D. The limit does not exist.

[1]
Select Answer

Question 5

Graphing calculator not permitted

For x0x\neq0, let

v(x)=x2sin(4x)v(x)=x^2\sin\left(\frac{4}{x}\right).

The graph of vv is shown together with the graphs of y=x2y=x^2 and y=x2y=-x^2 on [1,1][-1,1].

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Part (a)
[2]

Verify that

x2v(x)x2-x^2\leq v(x)\leq x^2

for every x0x\neq0.

Part (b)
[2]

Evaluate limx0(x2)\displaystyle\lim_{x\to0}(-x^2) and limx0x2\displaystyle\lim_{x\to0}x^2.

Part (c)
[2]

Justify the value of limx0v(x)\displaystyle\lim_{x\to0}v(x) using an appropriate theorem.

Part (d)(i)
[1]

Define

p(x)={v(x),x0,\k,x=0.p(x)=\begin{cases}v(x),&x\neq0,\k,&x=0.\end{cases}

Determine the value of kk that makes pp continuous at x=0x=0.

Part (d)(ii)
[2]

Verify that the three conditions for continuity at x=0x=0 are satisfied for this value of kk.

Question 6

Graphing calculator not permitted

A water-level sensor reports a reading R(t)R(t), in metres, over the time interval 0t80\leq t\leq8, where tt is measured in hours. The sensor output is continuous along each drawn curve or line segment. Open circles are not included function values, while filled points are included.

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Part (a)(i)
[2]

Estimate limt2R(t)\displaystyle\lim_{t\to2^-}R(t) and limt2+R(t)\displaystyle\lim_{t\to2^+}R(t).

Part (a)(ii)
[1]

Determine the type of discontinuity at t=2t=2. Justify your classification.

Part (b)(i)
[1]

Estimate limt5R(t)\displaystyle\lim_{t\to5}R(t).

Part (b)(ii)
[1]

Determine the value that should replace R(5)R(5) to remove the discontinuity.

Part (b)(iii)
[1]

Verify that the redefined function is continuous at t=5t=5.

Part (c)
[1]

After the repair in part (b), determine the maximal intervals on which the sensor function is continuous.

Part (d)
[2]

Justify that there is at least one time cc in (3,4.5)(3,4.5) at which R(c)=2R(c)=2.

Question 7

Graphing calculator not permitted

The graphs of functions ff and gg are shown. Both functions have removable discontinuities at x=2x=2. The filled circle represents f(2)f(2), and the filled square represents g(2)g(2).

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Part (a)
[2]

Calculate limx2(2f(x)3g(x))\displaystyle\lim_{x\to2}\left(2f(x)-3g(x)\right).

Part (b)
[2]

Calculate limx2f(x)g(x)\displaystyle\lim_{x\to2}\frac{f(x)}{g(x)} and verify that the quotient limit law applies.

Part (c)
[2]

Define

F(x)={f(x),x2,\k,x=2.F(x)=\begin{cases}f(x),&x\neq2,\k,&x=2.\end{cases} Determine the value of kk that makes FF continuous at x=2x=2.

Part (d)
[3]

Determine whether

limx2f(x)g(x)=f(2)g(2)\displaystyle\lim_{x\to2}\frac{f(x)}{g(x)}=\frac{f(2)}{g(2)}.

Calculate both quantities and explain your conclusion.

Question 8

Graphing calculator not permitted

The graph of a function ff is shown. The dashed lines are asymptotes of ff. Define

h(x)=1f(x)h(x)=\frac{1}{f(x)}

at every value of xx for which this expression is defined.

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Part (a)(i)
[2]

Determine limx1h(x)\displaystyle\lim_{x\to1^-}h(x) and limx1+h(x)\displaystyle\lim_{x\to1^+}h(x).

Part (a)(ii)
[1]

Evaluate limx1h(x)\displaystyle\lim_{x\to1}h(x).

Part (b)
[2]

Determine the vertical asymptote of hh. Justify your answer using the behaviour of ff.

Part (c)
[2]

Determine the horizontal asymptote of hh. Justify your answer using limits at infinity.

Part (d)
[1]

Represent the intervals on which hh is continuous.

Part (e)
[1]

Determine the value that could be assigned to h(1)h(1) to make hh continuous at x=1x=1.

Question 9

Graphing calculator not permitted

The graph of ff on [3,4][-3,4] consists of line segments. The function is continuous except at x=1x=1, where the open circle shows the limiting value and the filled point shows f(1)f(1).

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Part (a)
[3]

Verify the hypotheses of the Intermediate Value Theorem on [3,1][-3,-1] and justify that there is at least one c(3,1)c\in(-3,-1) for which f(c)=0f(c)=0.

Part (b)
[2]

Determine whether the Intermediate Value Theorem can be used on [0,2][0,2] to guarantee a solution to f(x)=2f(x)=2. Explain your answer.

Part (c)
[2]

Justify that there is at least one c(2,4)c\in(2,4) for which f(c)=1f(c)=1.

Part (d)
[2]

Explain why the Intermediate Value Theorem alone does not prove that the solution in part (c) is unique.

Question 10

Graphing calculator not permitted

The graph of ff is shown. Define

g(x)={f(x),x2,\2a1,x=2.g(x)=\begin{cases}f(x),&x\neq2,\2a-1,&x=2.\end{cases}

For which value of aa is gg continuous at x=2x=2?

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A. 32\frac32

B. 22

C. 52\frac52

D. 44

[1]
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