Fundamentals of Mathematics, 2008a

594 CHAPTER 10. SIGNED NUMBERS
Thus, (−4) + (−9) = −13.
10.5.2.2 Practice Set A
Find the sums.
Exercise 10.5.1 (Solution on p. 623.)
8 + 6
Exercise 10.5.2 (Solution on p. 623.)
41 + 11
Exercise 10.5.3 (Solution on p. 623.)
(−4) + (−8)
Exercise 10.5.4 (Solution on p. 623.)
(−36) + (−9)
Exercise 10.5.5 (Solution on p. 623.)
−14 + (−20)
Exercise 10.5.6 (Solution on p. 623.)
− 2 3 + ( )
− 5 3
Exercise 10.5.7 (Solution on p. 623.)
−2.8 + (−4.6)
Exercise 10.5.8 (Solution on p. 623.)
0 + (−16)
10.5.3 Addition With Zero
Addition with Zero
Notice that
(0) + (a positive number) = (that same positive number).
(0) + (a negative number) = (that same negative number).
The Additive Identity Is Zero
Since adding zero to a real number leaves that number unchanged, zero is called the additive identity.
10.5.4 Addition of Numbers with Unlike Signs
The addition 2 + (−6), two numbers with unlike signs, can also be illustrated using the number line.
Begin at 0, the origin.
Since 2 is positive, move 2 units to the right.
Since -6 is negative, move, from 2, 6 units to the left.
We are now located at -4.
We can suggest a rule for adding two numbers that have unlike signs by noting that if the signs are disregarded,
4 can be obtained by subtracting 2 from 6. But 2 and 6 are precisely the absolute values of 2 and
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