Chapter 1 - Foundations for Algebra - 1-5 Adding and Subtracting Real Numbers - Practice and Problem-Solving Exercises - Page 34: 35

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There are two key things to note here. First, it is important to remember that subtracting a negative is the same as addition. Thus, it follows that: $-7-(-5)=-7+5$ Second, we must recall that a negative becomes more positive when a positive number is added to it. Thus, we obtain: $-7+5=-2$