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| | 10 Theory slides |
| | 10 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
Here are a few practice exercises before getting started with this lesson.
A university is developing an eco-friendly battery for tablets called Flora, which uses no harmful chemicals for the environment. After running some tests, the following number line describes the results. Fully charged, the point at 10 indicates the average amount of hours a Flora battery lasts. The points at 8 and 12 indicate the minimum and maximum performance times, respectively.
Think of a mathematical model that needs to predict a strictly positive quantity. Ever wonder exactly how many days until the end of school, but are only given the calendar date? Well, consider a formula that counts the number of days. A date is entered into the formula and the prediction of 20 days away from today is made.
Then, another date is entered, but this time the formula says that it is - 30 days away!
Considering the given information about the formula, try to answer the following questions.
The absolute value of a number a is the distance between a and 0 on the number line. It is denoted as |a| and it is always a non-negative value.
There are several properties and identities that are useful when simplifying expressions or solving equations dealing with absolute values. For any two real numbers a and b, the following relationships and identities hold true.
| Property | Algebraic Representation |
|---|---|
| Non-negativity | |a| ≥ 0 |
| Symmetry | | - a| = |a| |
| Idempotence | ||a|| = |a| |
| Positive-definiteness | |a| = 0 ⇔ a = 0 |
| Identity of Indiscernibles | |a − b| = 0 ⇔ a = b |
| Multiplicativity | |ab| = |a| * |b| |
| Preservation of Division | |a/b|=|a|/|b| if b ≠ 0 |
| Subadditivity | |a + b| ≤ |a| + |b| |
| Triangle Inequality | |a − b| ≤ |a − c| + |c − b| |
Practice simplifying absolute value expressions by using the following applet.
An absolute value equation is an equation that involves the absolute value of a variable expression. | 2x-8 |=5 Equations of the form |x|=a, where a is a real number greater than zero, can be solved by looking for the numbers x whose distance from 0 in the number line equals a. For example, the solutions of |x|=4 are all values of x that are 4 units away from 0.
Since there are two points on the number line that fulfill this requirement, there are two solutions to the equation |x|=4, namely x=4 and x=- 4. However, solving an absolute value equation, in general, might require a more elaborate and structured approach.
Simple absolute value equations of the form |x|=a, can have no, one, or two solutions, depending on the value of a. However, more complex absolute value equations may have more than two solutions.
| Equation | Number of Solutions | Solution(s) |
|---|---|---|
| |x|=- 4 | Zero | No solution |
| |x|=0 | One | 0 |
| |x|=4 | Two | - 4, 4 |
| |x^2-4 |=2 | Four | - sqrt(2), sqrt(2), - sqrt(6), sqrt(6) |
An absolute value equation can be solved algebraically by first isolating the absolute value expression. Then, consider the two possible cases for the argument inside the absolute value: one where it is positive and one where it is negative. These lead to two separate linear equations, which can be solved independently. The following example will illustrate this process. |2x+4|-16=0 To solve an absolute value equation, there are four steps to follow.
| 2x+4=16 | 2x+4=-16 |
|---|---|
| 2x=12 | 2x=-20 |
| x=12/2 | x=-20/2 |
| x=6 | x=-10 |
Practice solving absolute value equations by using the following applet. Indicate which number line represents the solution set of the given equation.
Davontay is on a train trip to a school of magic. His smartphone is powered by an eco-friendly battery, but still a young product, it easily loses reception. A vendor notices and gives him hope. She exclaims, "Don't worry, lad. When the train is 60 kilometers near the next wizard village, the phone will get signal. It will last until the train is 60 kilometers past that village."
It is helpful to summarize the important information in a diagram. Recall that the train is originally 150 kilometers away from the next wizard village, and the smartphone will only get a signal when the distance of the train from the village is equal to 60 kilometers.
From the diagram, it can be seen that the train needs to cover a distance of 150-60=90 kilometers for the smartphone to recover its signal. By using the speed formula, the time of travel for that distance can be calculated.
Therefore, the phone will recover its signal after 30 minutes. Now, to determine how long it will keep connected, the time the train will take to leave the 60 kilometers proximity from the wizard village should be found.
As can be seen, the train needs to cover a distance of 150+60=210 kilometers for the smartphone to lose connection again. Now the formula for speed will be used once more. Recall that t was already isolated in the previous calculations. This result will be reused.
Hence, the smartphone will lose connection, once again, after 70 minutes of traveling. Taking into account that it will recover connection after the first 30 minutes, it can be concluded that it will remain connected for 70-30=40 minutes in total.
It is known that Davontay's distance from the next village is 150 kilometers. Since the train is moving, his distance is decreasing each minute by 3 kilometers. Using this information, Davontay's distance from the city can be written in terms of the time variable t. distance = 150-3t However, since the distance from the village is a length, it must be a non-negative quantity. This can be be assured by taking the absolute value of the expression. distance = |150-3t| Next, the times when this distance between the train and the city is exactly 60 kilometers should be calculated. This can be done by setting up the following equation. |150-3t| = 60 Since the constant at the right-hand side of the equation is positive, solving the equation is equivalent to solving two individual equations.
Now, the first equation will be solved.
Therefore, one of the solutions to the original absolute value equation is t=70. Now, the remaining equation will be solved.
Consequently, the train will be 60 kilometers away from the city on two occasions. Once, after traveling for 30 minutes while approaching the village. Secondly, after traveling 70 minutes having already passed, and moving away from the village. Therefore, the phone will stay connected for a total of 70-30=40 minutes.
Davontay is stoked to buy this video game console that is energized by an eco-friendly battery — everyone wants one. Davontay has $280 saved for this console, but its average selling price is $350. Shopping online, he uses a search program designed to find discounts. He finds that the differences in prices can be modeled with an absolute value equation.
The solutions for this absolute value equation represent the minimum and maximum prices for the console found online. Davontay is planning to buy it at the lowest price. How much more money does Davontay need to save so he can afford the lowest price found online according to this model?
As has been determined, according to the model, the minimum price at which the console can be purchased online is $305. The difference between the minimum price and what Dylan has saved $285 is $25. Therefore, Davontay needs to save $25 more to be able to buy the game console he has long awaited.
A university is developing an eco-friendly battery for tablets called Flora
that uses no harmful chemicals for the environment. After running some tests, the following number line describes the results. Fully charged, the point at 10 indicates the average amount of hours a Flora battery lasts. The points at 8 and 12 indicate the minimum and maximum performance times, respectively.
The university wants to report the specifications of the Flora battery's performance by using an algebraic expression. Let x represent the number of hours the battery can be used when fully charged. Then, find an equation that models the situation and whose solutions are the minimum and the maximum hours the battery can last.
As it can be seen from the diagram above, the average value of 10 is two units away from both the minimum and the maximum performance values. Note that the distance of an unknown value x from 10 in a number line can be calculated as a difference of those values. cc if x ≥ 10 & Distance: &x-10 & Example& x = 12 & Distance: &12-10 = 2 if x <10 & Distance: &10-x & Example& x = 8 & Distance: &10-8 = 2 Next, to write the distance in the form of an absolute value expression, the inequalities will be rewritten to have zeros on the right-hand sides resemble the definition for the absolute value of a quantity. x≥ 10 &⇔ x-10≥ 0 [1em] x < 10 &⇔ x-10 < 0 Also, note that 10-x is equivalent to - (x-10). All of these observations can be summarized in the following manner. Distance= x-10 & if x - 10 ≥ 0 - (x-10) & if x - 10 < 0 Notice that this formula for the distance is now very similar to the definition of the absolute value of a number. Therefore, all the previous information imply that the distance for a value x from 10 is |x-10|. Distance=|x -10| Finally, since it is known that the distance to the desired values is 2, the required equation can be set up. 2=|x-10| ⇕ |x-10|=2 Now that the Flora battery has been tested and the performance results can be reported using a formal mathematical expression, the university can let everyone know about Flora to power devices in a cleaner way!
We will calculate the expression by first simplifying what is inside the absolute value. After this, we can remove the absolute value. Since the absolute value of a number is always non-negative, if the simplified expression is negative, it will become positive when the absolute value is removed. If it is already positive, it will remain unchanged.
We found that the expression simplifies to 5.
As in Part A, we start by simplifying the expression inside the absolute value. Then we remove the absolute value and change the sign of the expression to to positive if the simplified expression inside the absolute value is negative.
We found that the expression simplifies to 2.
Let's follow the same procedure to simplify the expression and then remove the absolute value. Remember, the absolute value of an expression is never negative.
We found that the expression simplifies to 1.
Consider the following number lines.
Pair the graphs with the correct absolute value equation i. & |x+2 |=4 [0.5em] ii. & |x-4|=2 [0.5em] iii. & |x+4|=2 [0.5em] iv. & |x-2 |=4
When we know two points on a number line and their midpoint, we can write an absolute value equation. The equation is written on the following format. |x- midpoint|= distance to midpoint Let's start by rewriting all equations to match this format. i. & |x-( -2) |= 4 [0.5em] ii. & |x- 4|= 2 [0.5em] iii. & |x-( -4)|= 2 [0.5em] iv. & |x- 2|= 4 Next, we will identify the midpoint and distance to each point in each of the graphs. After that, we can pair the graph with the correct equation. Let's begin with graph A.
With the information of the graph, we can write the absolute value equation of graph A. |x-( -4)| = 2 Therefore, graph A is associated with equation iii. Now let's take a look at graph B.
Now we can use this information to write the equation of graph B. |x-( -2)| = 4 Therefore, graph B is associated with equation i. Now we can go to graph C.
Using the information obtained, we can also write the equation of this graph. |x- 2| = 4 Therefore, graph C is associated with equation iv. Finally, we can look at graph D.
Now we can write the equation. |x- 4| = 2 Graph D is associated with equation ii. Now let's take a final look of all the pairings! A& → -1pt &&iii. B& → -1pt &&i. C& → -1pt &&iv. D& → -1pt &&ii.
Let's start by calculating all of the individual absolute values. Then we can add the results. Remember, since an absolute value is always non-negative, any argument that is negative changes signs and becomes positive.
Now that we found all the absolute values, we can add all the terms! 1+4+11 = 16
Again, we start by calculating all the individual absolute values. Remember that if the argument of an absolute value is negative, we need to change the sign for the argument to become positive.
Now we can add or subtract the results regularly. 99 - 17 + 180 = 262
As in previous parts, we will evaluate the absolute values and simplify the results. But we have to be careful, since if the result of an absolute value has a negative sing, the result is a negative number.
Now we can add and subtract the numbers regularly. - 2 + 11.5 - 7.5 = 2 Now we have finished. Good job!
An absolute value measures an expression's distance from a midpoint on a number line. |m+4|= 7 This equation means that the distance is 7, either in the positive direction or in the negative direction. Algebraically, we can separate the absolute value equation into two cases after the absolute value is removed, one case where 7 is positive and the other where it is negative. |m+4|= 7 ⇒ lm+4= 7 m+4= - 7 To find the solutions to the absolute value equation, we need to solve both of these cases for m.
We can see that m has to possible values. Let's write these answers from least to greatest. m_1 & = -11 m_2 & =3
As in Part A, we get two cases when we remove the absolute value.
Now we can see that x has to possible values. Let's write these answers from least to greatest. x_1 & = -7 x_2 & =23
As in previous parts, we get two cases when we remove the absolute value.
Again we can see that x has to possible values. Let's write these answers from least to greatest. x_1 & = -5 x_2 & =5
As in previous parts, we get two cases when we remove the absolute value.
This time we can also see that b has to possible values. Let's write these answers from least to greatest. b_1 & = -7 b_2 & =12
Before we can solve this equation, we need to isolate the absolute value expression.
An absolute value measures the distance from a midpoint on a number line. Note that a distance cannot be negative. This means the absolute value of a number must also be non-negative. |y-1|≠ -3 This absolute value equation has no solution.
Let's label the percentage of voters that are likely to vote for Candidate A v. The poll tells us that 55 % of voters, including a margin of error of 3 %, are likely to vote for the candidate. A margin of error indicates that the difference between the actual value v and 55 is ± 3. v - 55 = ± 3 The ± symbol indicates that the subtraction can be equal to -3 or 3. Note that we can rewrite this expression as two equations. v-55=-3 v-55= 3 If we look closely at these equations, we can see that this is how we separate the cases of an absolute value equation. Let's write the absolute value equation that results in these cases! |v-55|=3
In order to solve the absolute value equation, we start by to separating the equation back into its cases from Part A. Then we can solve each case equation individually. Let's do it!
Looking at the results, we can see that the least percent of voters who will vote for Candidate A is 52 %, and the greatest percent is 58 %.