Question

what is the sum of 9 and -9?
○ 0
○ 18
○ -18

Explanation:

Step1: Recall the rule for adding a number and its opposite

The sum of a number \( a \) and its additive inverse \( -a \) is \( 0 \). In formula, \( a + (-a)=0 \).

Step2: Apply the rule to the given numbers

Here, \( a = 9 \) and \( -a=-9 \). So, \( 9+(-9) \) is the sum of a number and its additive inverse. Using the rule from Step 1, we get \( 9+(-9) = 0 \).

Answer:

A. 0