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Using Absolute Value Lesson 2.2.2

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**Using Absolute Value 2.2.2 California Standards:**

Lesson 2.2.2 Using Absolute Value California Standards: Number Sense 2.5 Understand the meaning of the absolute value of a number; interpret the absolute value as the distance of the number from zero on a number line; and determine the absolute value of real numbers. Algebra and Functions 1.1 Use variables and appropriate operations to write an expression, an equation, an inequality, or a system of equations or inequalities that represents a verbal description (e.g., three less than a number, half as large as area A). What it means for you: You’ll use absolute value to find the difference between two numbers and see how absolute values apply to real-life situations. Key words: absolute value comparison difference

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Lesson 2.2.2 Using Absolute Value You use absolute value a lot in real life — often without even thinking about it. For example, if the temperature falls from 3 °C to –3 °C you might use it to find the overall change. This Lesson looks at some of the ways that absolute value can apply to everyday situations.

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**8 – 6 = 2, so 8 and 6 are 2 units apart.**

Lesson 2.2.2 Using Absolute Value Absolute Values Help Find Distances Between Numbers To find the distance between two numbers on the number line you could count the number of spaces between them. Using subtraction is a quicker way — just subtract the lesser number from the greater. 8 – 6 = 2, so 8 and 6 are 2 units apart. If you did the subtraction the other way around you’d get a negative number — and distances can’t be negative.

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Lesson 2.2.2 Using Absolute Value But if you use absolute value bars you can do the subtraction in either order and you’ll always get a positive value for the distance. |6 – 8| = |–2| = 2 and |8 – 6| = 2 This is particularly useful when you’re finding the distance between a positive and negative number. For any numbers a and b: The distance between a and b on the number line is |a – b|.

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**Using Absolute Value 2.2.2 What is the distance between –3 and 5?**

Lesson 2.2.2 Using Absolute Value Example 1 What is the distance between –3 and 5? Solution The distance between –3 and 5 is | –3 – 5 | = | –8 | = 8. Distance of 8 1 2 3 –1 –2 –3 –4 –5 –6 4 5 6 Solution follows…

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**Using Absolute Value 2.2.2 Guided Practice**

Lesson 2.2.2 Using Absolute Value Guided Practice Find the distance between the numbers given in each of Exercises 1– , –3, –8 3. 6, – –1, 10 5. 3, – , –1 7. –1.2, –0.3, 2.7 9. At 1 p.m., Amanda was 8 miles east of her home. She then traveled in a straight line west until she was 6 miles west of her home. How many miles did she travel? 4 5 15 11 8 6 3.5 3 14 miles Solution follows…

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**Using Absolute Value 2.2.2 Absolute Values are Used to Compare Things**

Lesson 2.2.2 Using Absolute Value Absolute Values are Used to Compare Things You can use absolute values to compare numbers when it doesn’t matter which side of a fixed point they are.

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**Using Absolute Value 2.2.2 Point A = 50 m (above sea level)**

Lesson 2.2.2 Using Absolute Value Example 2 Point A = 50 m (above sea level) Find how far point A is above point B. Sea level = 0 m Solution It doesn’t matter that B is below sea level and A is above. It’s the distance between them that’s important. Point B = –35 m (below sea level) You can find this using: |50 m – (–35 m)| = |85 m| = 85 m. You’d get the same answer if you did the subtraction the other way around: |–35 m – 50 m| = |–85 m| = 85 m. Solution follows…

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**Using Absolute Value 2.2.2 Guided Practice**

Lesson 2.2.2 Using Absolute Value Guided Practice 10. A miner digs the shaft shown. What distance was he from the top of the crane when he finished digging? 20 ft 0 ft –10 ft –20 ft –30 ft –40 ft –50 ft |–50 – 20| = |–70| = 70 ft 11. The top of Mount Whitney is 14,505 ft above sea level. The bottom of Death Valley is 282 ft below sea level. How much higher is the top of Mount Whitney than the bottom of Death Valley? |14,505 – (–282)| = |14,787| = 14,787 ft Solution follows…

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**Using Absolute Value 2.2.2 Absolute Values Can Describe Limits**

Lesson 2.2.2 Using Absolute Value Absolute Values Can Describe Limits Another use of absolute values is to describe the acceptable limits of a measurement. It might not be important whether something is above or below a set value, but how far above or below it is.

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Lesson 2.2.2 Using Absolute Value Example 3 The average temperature of the human body is 98.6 °F, but in a healthy person it can be up to 1.4 °F higher or lower. The difference between a person’s temperature, x, and the average healthy temperature can be found using |98.6 – x|. Aaron is feeling unwell so measures his temperature. It is °F. Is Aaron’s temperature within the healthy range? Solution The difference between Aaron’s temperature and the average healthy temperature is |98.6 – 100.2| = |–1.6| = 1.6 °F. Aaron’s temperature is outside of the normal healthy range. Solution follows…

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**Using Absolute Value 2.2.2 Lesson Example 4**

A factory manufactures wheels that it advertises as no more than 1 inch away from 30 inches in diameter. They use the expression |30 – d| to test whether wheels are within the advertised size (where d is the diameter). Apply the expression to wheels of diameters 31, 29, and 35 inches, and say whether they meet the advertised standard. Solution Wheel of diameter 31 inches: |30 – 31| = |–1| = 1 inch. This wheel is within the standard. Wheel of diameter 29 inches: |30 – 29| = |1| = 1 inch. This wheel is within the standard. Wheel of diameter 35 inches: |30 – 35| = |–5| = 5 inches. This wheel is not within the standard. Solution follows…

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**Using Absolute Value 2.2.2 Guided Practice**

Lesson 2.2.2 Using Absolute Value Guided Practice 12. The height of a cupboard door should be no more than 0.05 cm away from 40 cm. The expression |40 – h| is used to check whether a door of height h cm fits the size requirement. If a door measures cm, is it within the correct range? 13. Ms. Valesquez’s car needs a tire pressure, p, of 30 psi. It should be within 0.5 psi of the recommended value. She uses the expression |30 – p| to test whether the pressure is acceptable. Is a pressure of 29.4 psi acceptable? |40 – | = It is within the correct range. |30 – 29.4| = This isn’t an acceptable pressure. Solution follows…

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**Using Absolute Value 2.2.2 Independent Practice**

Lesson 2.2.2 Using Absolute Value Independent Practice Find the distance between the numbers given in each of Exercises 1– , – , –4 3. 5, –32, –52 5. The table below shows the temperature at different times of day. How much did the temperature change by between 7 a.m. and 8 a.m.? 18 7 1 20 6 °C 1 °C –5 °C Temperature 8 a.m. 7 a.m. Time Solution follows…

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**Using Absolute Value 2.2.2 Independent Practice**

Lesson 2.2.2 Using Absolute Value Independent Practice 6. A person stands on a pier fishing. The top of their rod is 20 feet above sea level. The line goes vertically down and hooks a fish 13 feet below sea level. How long is the line? 7. Priscilla tries to keep the balance of her checking account, b, always less than $50 away from $200. She uses the expression |200 – b| to check that it is within these limits. Is a balance of $ acceptable? 33 feet |200 – | = This is an acceptable balance. Solution follows…

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**Using Absolute Value 2.2.2 Round Up**

Lesson 2.2.2 Using Absolute Value Round Up Absolute values are used to find distances between numbers. They’re also useful when measurements are only allowed to be a certain distance away from a set value. In these situations, it doesn’t matter if the numbers are above or below the set point — it’s how far away they are that’s important.

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