This document provides guidance and examples for evaluating variable expressions by: 1) Substituting values for variables and evaluating based on order of operations. Examples show evaluating expressions like 15 - a - b when a and b are given values. 2) Guiding practice problems for students to evaluate expressions like a - b - (-6) by substituting values for a and b. 3) More examples of evaluating expressions like x - y + 8 by substituting given values for x and y. 4) Reminders to be careful of absolute value signs and whether to subtract or evaluate absolute value first in expressions like 3 - |-2|.

1. Day Two of Subtracting Reals Using Variable Expressions Word Problems / Applications

2. EXAMPLE 2 Evaluating a Variable Expression Evaluate 15 –a –bwhen a = 24 and b = – 36 . 15 – a – b= 15 – 24–(–36) Substitute 24 for ad –36 for b. Add the opposite of 24 and of –36. = 15 + (–24) + 36 = –9 + 36 Add 15 and –24. = 27 Add –9 and 36.

3. for Examples 1, 2, and 3 GUIDED PRACTICE a – b – (–6); a = 8, b = –15 a – b–(–6) = 8–(–15) – 6 Substitute 8 for aand –15 for b. Add the opposite of–15 and of –6. = 8 +15+6 = 29 Add.

4. x – y + 8 y – (x –2) 4. 5. for Example 2 and 3 GUIDED PRACTICE Evaluate the expression when x = – 3 and y = 5.2. =– 3– (5.2) + 8 Write an equation. Substitute values. =– 3 + (–5.2 )+ 8 Add the opposite of –5.2 =–0.2 Add =5.2– (–3 – 2) Write an equation. Substitute values. =5.2 –(– 3 +(– 2 )) Add the opposite of –2 Add the result =5.2 + – (– 5) =10.2 Add

5. Watch out for absolute value signs.Should you subtract first or do the absolute value of the number first? 3 - |-2| = -7 - |16| = |-12| - |-20| =

6. Cont’ P. 82-83 (#15-25, 38-40, 42-45) You may work with a partner if you work quietly. Study for Quiz tomorrow 2.1-2.3