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Applied Precalculus MTH 103

Appendix A Selected Solutions

1 Introduction to Functions
1.1 The Concept of a Function
Practice Problems

2.

Solution.
The independent variable is \(t\) and has units of years. The dependent variable is \(V\) and has units of dollars.

Exercises

1.

Solution.
  1. The amount of caffeine in a person’s body \(0\) hours after drinking a cup of coffee is 96 mg.
  2. The amount of caffeine in a person’s body \(5\) hours after drinking a cup of coffee is 48 mg.
  3. The amount of caffeine in a person’s body \(24\) hours after drinking a cup of coffee is approximately 0 mg.

2.

Solution.
  1. A total of 10 units of the product are produced in 1 hour.
  2. A total of 0 units of the product are produced in 0 hours.
  3. A total of approximately 29 units of the product are produced in 3 hours.

4.

Solution.
  1. The independent variable is \(t\text{,}\) which represents the time spent baking in hours.
  2. The dependent variable is \(B\text{,}\) which represents the number of batches of cookies made by the bakery after \(t\) hours have passed.
  3. \(f(3)=18\text{;}\) The bakery makes 18 batches of cookies (or approximately 216 cookies) in 3 hours.

5.

Solution.
  1. The amount of fuel left in the fuel tank 70 miles into the drive is 6 gallons.
  2. The amount of fuel left in the fuel tank 200 miles into the drive is 1 gallon.

20.

Solution.
  1. all real numbers or \((-\infty,\infty)\) in interval notation
  2. all real numbers \(x\neq1\) or \((-\infty,1)\cup(1,\infty)\) in interval notation
  3. all real numbers \(x\neq-2\text{,}\) \(x\neq2\) or \((-\infty,-2)\cup(-2,2)\cup(2,\infty)\) in interval notation
  4. all real numbers \(x\geq0\) or \([0,\infty)\) in interval notation
  5. all real numbers or \((-\infty,\infty)\) in interval notation

21.

Solution.
  1. all real numbers or \((-\infty,\infty)\) in interval notation
  2. all real numbers \(x\neq0\) or \((-\infty,0)\cup(0,\infty)\) in interval notation
  3. all real numbers \(x\gt 0\) or \((0,\infty)\) in interval notation

1.2 The Graph of a Function
Exercises

1.

Solution.
\(x\) \(-2\) \(-1\) \(0\) \(1\) \(2\)
\(y\) \(-8\) \(-1\) \(0\) \(1\) \(8\)
A short description.

2.

Solution.
\(t\) \(-2\) \(-1\) \(0\) \(1\)
\(f(t)\) \(2\) \(0\) \(0\) \(2\)
A short description.

3.

Solution.
\(x\) \(0\) \(1\) \(4\) \(9\)
\(g(x)\) \(0\) \(1\) \(2\) \(3\)
A short description.

4.

Solution.
\(p\) \(10\) \(12\) \(14\) \(16\) \(18\) \(20\)
\(C\) \(12\) \(14.4\) \(16.8\) \(19.2\) \(21.6\) \(24\)
A short description.

7.

Solution.
\(x\approx -1.5\text{,}\) \(x=0\text{,}\) and \(x\approx 4.5\text{.}\)

16.

Solution.
Increasing on the intervals \((0,3) \cup (9,12)\text{.}\) Or, write as \(0\lt t\lt 3\) and \(9\lt t\lt 12\). Decreasing on the interval \((3,9)\text{.}\) Or, write as \(3\lt t \lt 9\).

1.3 Functions Given Numerically

Exercises

1.3.7.
Solution.
\(d\) \(180\) \(216\) \(252\)
\(G(d)\) \(11\) \(9.5\) \(8\)
The gas mileage of the driver’s Volkswagen Passat is 24 miles per gallon.
1.3.8.
Solution.
\(t\) \(0\) \(1\) \(2\) \(3\) \(4\) \(5\) \(6\) \(7\) \(8\)
\(P(t)\) \(6.957\) \(7.041\) \(7.126\) \(7.211\) \(7.296\) \(7.380\) \(7.464\) \(7.548\) \(7.631\)
1.3.10.
Solution.
  1. The amount of power required for the dragon to carry the knight is increasing as the dragon’s speed increases. This is evident from the table since the values associated with the power required increase as the speed increases.
  2. The amount of power required for the dragon to carry the knight is increasing faster and faster as the dragon’s speed increases. This is evident from the table since each time the speed increases by 10 miles per hour starting at 60 miles per hour, the power required to carry the knight increases by more and more.
1.3.11.
Solution.
A short description.
  1. The amount of power required for the dragon to carry the knight is increasing as the dragon’s speed increases. This is evident from the graph since it climbs over the interval \(60\leq x \leq 100\text{.}\)
  2. The amount of power required for the dragon to carry the knight is increasing faster and faster as the dragon’s speed increases. This is evident from the graph since each time the speed increases by 10 miles per hour starting at 60 miles per hour, the graph climbs more and more quickly.

1.4 Vertical and Horizontal Intercepts

Exercises

1.4.1.
Solution.
  1. horizontal intercept: \(0.5\text{;}\) vertical intercept: \(-1.5\)
  2. horizontal intercepts: \(-1\text{,}\) \(1\text{;}\) vertical intercept: \(1\)
  3. horizontal intercept: \(27\text{;}\) vertical intercept: \(5.4\)
  4. horizontal intercept: \(-2\text{;}\) vertical intercept: \(16\)
  5. horizontal intercept: \(9/4\text{;}\) vertical intercept: \(-3\)
  6. horizontal intercepts: none; vertical intercept: none
  7. horizontal intercept: none; vertical intercept: \(-1\)
1.4.4.
Solution.
vertical intercept: 300β€”this is the number of feet above the lake that the ball is dropped from; horizontal intercept: \(t \approx 4.33\)β€”this is the number of seconds that it takes after being dropped for the ball to hit the surface of the lake
1.4.5.
Solution.
vertical intercept: 21500β€”this is the price in dollars for which the car was purchased; horizontal intercept: \(t \approx 14.33\)β€”this is the number of years after purchase that it takes for the car’s value to depreciate to \(\$0\)

1.5 The Average Rate of Change

Exercises

1.5.4.
Solution.
  1. \(-9.6\) mg/hr
  2. \(-2.4\) mg/hr
  3. The average rate of change from \(t = 0\) to \(t = 5\) hours is larger than the average rate of change from \(t=10\) to \(t=15\) hours. It can be seen that the rate at which the amount of caffeine in the bloodstream is changing gets smaller and smaller as time progresses.

2 Linear Functions
2.1 Properties of Linear Functions
Exercises

2.

Solution.
\(g(x)=8x-2\text{;}\) slope: \(8\text{;}\) vertical intercept: \(-2\)

3.

Solution.
\(h(t)=9t-2.5\text{;}\) slope: \(9\text{;}\) vertical intercept: \(-2.5\)

4.

Solution.
\(m(x)=2x\text{;}\) slope: \(2\text{;}\) vertical intercept: \(0\)

15.

Solution.
  1. slope: \(0.5\text{;}\) vertical intercept: \(1\text{;}\) equation: \(y=0.5x+1\)
  2. slope: \(-\frac{3}{2}\text{;}\) vertical intercept: \(-1\text{;}\) equation: \(y=-\frac{3}{2}x-1\)
  3. slope: \(\frac{2}{3}\text{;}\) vertical intercept: \(0\text{;}\) equation: \(y=\frac{2}{3}x\)
  4. slope: \(-\frac{2}{3}\text{;}\) vertical intercept: \(-1\text{;}\) equation: \(y=-\frac{2}{3}x-1\)

16.

Solution.
Line 1 is \(y=3x+2\text{;}\) Line 2 is \(y=3x-1\text{;}\) Line 3 is \(y = 2\text{;}\) Line 4 is \(y=x-1\text{;}\) Line 5 is \(y=-2x-3\text{.}\)

19.

Solution.
  1. The bicyclist’s initial distance from the finish line is 50 miles.
  2. The bicyclist’s distance from the finish line is decreasing at a rate of 25 miles per hour.

2.2 Working with Linear Functions and Linear Equations
Exercises

18.

Solution.
  1. The vertical intercept 60 is the distance in miles that the biker is from the finish line at the start of the race.
  2. The horizontal intercept 3 is the number of hours that it takes the biker to complete the race.
  3. The slope \(-20\) indicates that the distance between the biker and the finish line is decreasing at a rate of 20 miles per hour.

2.3 Modeling and Numerically Given Functions

Exercises

2.3.6.
Solution.
  1. Linear; formula \(H(t)=\frac{2}{3}t+85\)
  2. The slope is \(\frac{2}{3}\) bpm per minute; the practical meaning of the slope is that the man’s bpm is increasing at a rate of \(\frac{2}{3}\) bpm per minute. The vertical intercept is \(85\) bpm; the practical meaning of the vertical intercept is that the man’s resting heart rate (heart rate when performing no exercise on the treadmill) is \(85\) bpm.

3 Quadratic Functions
3.1 Introduction to Quadratic Functions
Exercises

5.

Solution.
horizontal intercepts: \(-1\text{,}\) \(3\text{;}\) vertical intercept: \(-3\text{;}\) vertex: \((1,-4)\)

6.

Solution.
no horizontal intercepts; vertical intercept: \(-2\text{;}\) vertex: \((1,-1)\)

10.

Solution.
  1. \(R(p)=p(1000-2p)\) or \(R(p)=-2p^2+1000p\)
  2. \(\displaystyle \$500\)
  3. The maximum revenue is \(\$125,000\text{.}\) The lighting company should charge \(\$250\) per specialty chandelier to maximize revenue.

3.2 Factoring Quadratic Expressions
Exercises

1.

Solution.
horizontal intercepts: \(-1\text{,}\) \(-2\text{;}\) vertical intercept: \(2\)

2.

Solution.
horizontal intercepts: \(-2\text{,}\) \(3\) ; vertical intercept: \(-6\)

3.

Solution.
horizontal intercepts: \(-3\text{,}\) \(2\) ; vertical intercept: \(-6\)

4.

Solution.
horizontal intercepts: \(4\text{;}\) vertical intercept: \(16\)

5.

Solution.
horizontal intercept: \(-7\text{;}\) vertical intercept: \(49\)

6.

Solution.
horizontal intercepts: \(-\frac{3}{4}\text{,}\) \(\frac{3}{4}\text{;}\) vertical intercept: \(-36\)

7.

Solution.
horizontal intercepts: \(-4\text{,}\) \(-1\text{;}\) vertical intercept: \(8\)

8.

Solution.
horizontal intercepts: \(-1\text{,}\) \(\frac{3}{2}\text{;}\) vertical intercept: \(-3\)

9.

Solution.
horizontal intercepts: \(-8\text{,}\) \(2\text{;}\) vertical intercept: \(16\)

10.

Solution.
horizontal intercepts: \(-\frac{1}{14}\text{,}\) \(\frac{1}{14}\text{;}\) vertical intercept: \(\frac{1}{49}\)

11.

Solution.
horizontal intercepts: \(0\text{,}\) \(3\text{;}\) vertical intercept: \(0\)

12.

Solution.
horizontal intercepts: \(0\text{,}\) \(\frac{2}{5}\text{;}\) vertical intercept: \(0\)

3.3 Vertex Form and Completing the Square
Exercises

5.

Solution.
\(f(x)=x^2+2x+3\text{;}\) \(a=1\text{,}\) \(b=2\text{,}\) \(c=3\)

6.

Solution.
\(g(x)=5x^2-20x+26\text{;}\) \(a=5\text{,}\) \(b=-20\text{,}\) \(c=26\)

7.

Solution.
\(y=-2t^2+16t-27\text{;}\) \(a=-2\text{,}\) \(b=16\text{,}\) \(c=-27\)

8.

Solution.
\(h(x)=-x^2-x+\frac{17}{12}\text{;}\) \(a=-1\text{,}\) \(b=-1\text{,}\) \(c=\frac{17}{12}\)

11.

Solution.
\(h(x)=\left(x+\frac{3}{2}\right)^2-1\text{;}\) vertex \(\left(-\frac{3}{2},-1\right)\)

18.

Solution.
\(-2-\sqrt{10}\approx-5.162\text{,}\) \(-2+\sqrt{10}\approx1.162\)

20.

Solution.
\(-4-\sqrt{\frac{5}{2}}\approx-5.581\text{,}\) \(-4+\sqrt{\frac{5}{2}}\approx-2.419\)

3.4 The Quadratic Formula
Exercises

4.

Solution.
\(x=1-\sqrt{3}\approx-0.732\) and \(x=1+\sqrt{3}\approx2.732\)

6.

Solution.
\(x=\dfrac{1-\sqrt{41}}{2}\approx-2.701\) and \(x=\dfrac{1+\sqrt{41}}{2}\approx3.702\)

7.

Solution.
horizontal intercepts: \(-3\text{,}\) \(1\text{;}\) vertical intercept: \(-3\text{;}\) vertex: \((-1,-4)\)

8.

Solution.
horizontal intercepts: \(-4-\sqrt{6}\approx-6.450\text{,}\) \(-4+\sqrt{6}\approx-1.551\text{;}\) vertical intercept: \(10\text{;}\) vertex: \((-4,-6)\)

9.

Solution.
horizontal intercepts: \(\frac{3-2\sqrt{3}}{3}\approx-0.155\text{,}\) \(\frac{3+2\sqrt{3}}{3}\approx2.155\text{;}\) vertical intercept: \(-1\text{;}\) vertex: \((1,-4)\)

10.

Solution.
no horizontal intercepts; vertical intercept: 5; vertex \((2,1)\)

15.

Solution.
  1. \(\displaystyle H(t)=-16t^2+50t+6\)
  2. The ball reaches its maximum height approximately 1.56 seconds after it is thrown straight up and that maximum height is approximately 45.06 feet.

17.

Solution.
\(g(x)=\left(x-(-3-\sqrt{2})\right)\left(x-(-3+\sqrt{2})\right)\)

4 Power Functions
4.1 Algebra of Powers: Integral Exponents

Exercises

4.1.16.
Solution.
\begin{align*} (a^p)^r \amp = \left( \underbrace{a \cdot a \cdot \ldots \cdot a}_{p \text{ times}}\right)^r\\ \amp = \underbrace{\left( \underbrace{a \cdot a \cdot \ldots \cdot a}_{p \text{ times}}\right) \cdot \ldots \cdot \left( \underbrace{a \cdot a \cdot \ldots \cdot a}_{p \text{ times}}\right)}_{r \text{ times}}\\ \amp= \underbrace{a \cdot a \cdot \ldots \cdot a}_{p \cdot r \text{ times}}\\ \amp= a^{p\cdot r} \end{align*}

4.2 Algebra of Powers: Fractional Exponents
Exercises

1.

Solution.
\(x=-\sqrt[4]{20}\approx-2.115\) and \(x=\sqrt[4]{20}\approx2.115\)

2.

Solution.
\(b=-\sqrt[30]{\frac{34}{3}} \approx -1.084\) and \(b=\sqrt[30]{\frac{34}{3}} \approx 1.084\)

5.

Solution.
\(x=1-\sqrt{3}\approx-0.732\) and \(x=1+\sqrt{3}\approx2.732\)

4.3 Power Functions: Positive Integral Exponents
Exercises

14.

Solution.
A is \(y=x^4\text{;}\) B is \(y=-x^4\text{;}\) C is \(y=\frac{1}{4}^4\text{.}\)

4.4 Power Functions: Fractional and Negative Integral Exponents
Exercises

3.

Solution.
\(y=\frac{1}{4}x^{17/12}\text{;}\) \(k=\frac{1}{4}\text{;}\) \(p=\frac{17}{12}\)

5.

Solution.
\(y=\frac{1}{3}x^2\text{;}\) \(k=\frac{1}{3}\text{;}\) \(p=2\)

10.

Solution.
Graph A is \(y=2 x^{1/2}\text{,}\) graph B is \(y=x^{1/2}\text{,}\) and graph C is \(y=-x^{1/2}\text{.}\)

13.

Solution.
  1. yes; \(T=\dfrac{2\pi}{\sqrt{g}}L^\frac{1}{2}\) where the coefficient is \(\dfrac{2\pi}{\sqrt{g}}\) and the exponent is \(\frac{1}{2}\text{.}\)
  2. approximately \(1.42\) seconds.
  3. approximately \(0.47 \text{ m}/\text{sec}^2\text{.}\)