Fundamentals of Mathematics, 2008a

652 CHAPTER 11. ALGEBRAIC EXPRESSIONS AND EQUATIONS
equation by −1.
(−1) (−x) = −1 · 7
x = −7
Check: When x = 7,
−x = 7
becomes
The solution to −x = 7 is x = −7.
11.5.2.2 Practice Set A
Use the multiplication/division property of equality to solve each equation. Be sure to check each solution.
Exercise 11.5.1 (Solution on p. 686.)
7x = 21
Exercise 11.5.2 (Solution on p. 686.)
−5x = 65
Exercise 11.5.3 (Solution on p. 686.)
x
4 = −8
Exercise 11.5.4 (Solution on p. 686.)
3x
8 = 6
Exercise 11.5.5 (Solution on p. 686.)
−y = 3
Exercise 11.5.6 (Solution on p. 686.)
−k = −2
11.5.3 Combining Techniques in Equation Solving
Having examined solving equations using the addition/subtraction and the multiplication/division principles
of equality, we can combine these techniques to solve more complicated equations.
When beginning to solve an equation such as 6x − 4 = −16, it is helpful to know which property of equality
to use rst, addition/subtraction or multiplication/division. Recalling that in equation solving we are trying
to isolate the variable (disassociate numbers from it), it is helpful to note the following.
To associate numbers and letters, we use the order of operations.
1. Multiply/divide
2. Add/subtract
To undo an association between numbers and letters, we use the order of operations in reverse.
1. Add/subtract
2. Multiply/divide
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