Читать книгу Basic Math & Pre-Algebra All-in-One For Dummies (+ Chapter Quizzes Online) - Mark Zegarelli - Страница 59

Suppose you want to calculate . You already know to start at , but where do you go from there? Here’s the up and down rule for adding a negative number:

Adding a negative number is the same as subtracting a positive number — go down on the number line.

By this rule, is the same as , so start at , down :

If you rewrite a subtraction problem as an addition problem — for instance, rewriting you can use the commutative and associative properties of addition, which I discuss earlier in this chapter. Just remember to keep the negative sign attached to the number when you rearrange the problem: .