Читать книгу Basic Math & Pre-Algebra All-in-One For Dummies (+ Chapter Quizzes Online) - Mark Zegarelli - Страница 58

When you’re adding and subtracting on the number line, starting with a negative number isn’t much different from starting with a positive number. For example, suppose you want to calculate . Using the up and down rule, you start at and go up :

Similarly, suppose you want to calculate . Again, the up and down rule helps you out. You’re subtracting, so move to the left: start at , down :

.