Big Ideas Math: Modeling Real Life, Grade 7
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Big Ideas Math: Modeling Real Life, Grade 7 View details
Cumulative Practice

Exercise 4 Page 43

Subtracting can be thought of as going left on the number line.

25

We want to determine the value of the given expression. 17-( - 8) We can recall that subtracting a positive number is the same as adding its opposite. 17-( - 8) ⇔ 17+8 Finally, we can perform the addition. 17+8= 25 We can see that adding a negative number is the same as subtracting its positive counterpart. Below we can demonstrate this by finding the difference between 17 and - 8 on the number line. Let's draw an arrow from 0 to 17 on the the number line!

Next we can draw an arrow 8 units to the left to represent subtracting - 8.

The expression has the value of 25.

Extra

Properties of Real Numbers

When we are performing mathematical operations using real numbers, we always need to make sure that we are following the Properties of Real Numbers.

These properties tell us the legal moves we can make when adding or multiplying numbers.

But why aren't there properties for subtraction or division?

Some mathematicians refuse to acknowledge that subtraction and division are even operations! Subtraction is the same thing as adding a negative and division is the same thing as multiplying by a fraction. a-b=a+(- b) and a/b=a* 1/b Therefore, we can use the Properties of Real Numbers for subtraction and division, but we need to change our way of thinking.