To figure out this problem, you can look at formulas, or you can try out a few problems. There are many people that prefer one or the other in my class, so I will show you both. :)
Before I show you either of these, I'm going to define rational numbers and explain some things so that you can understand why we do what we do. Make sure to remember things like this because when you get to algebra (I'm in algebra), you need to know all of this stuff! :)
A rational number is any number that can be written in a over b form (a/b) or as a fraction. A rational number can be positive or negative because you can put positive and negative numbers into a fraction. Decimals can also be rational numbers because things such as .3 can be written as 3/10. So, depending on what number you have, there is always an opposite.
To find an opposite number, you have to basically find the absolute value (how far the number is from zero), double that number, and add it from the original number. Or, if you want to make it worlds easier, you can just make the number the opposite inverse. So, if it is -4, the opposite is 4. If the number is 7, then the opposite is -7. What is the sum between both of those examples? Zero.
Here is the formula: a+(-a)=0, (-a)+a=0
Here is some examples: (-5)+5=0, 8+(-8)=0
Thanks so much for the opportunity to answer your question. I hope this helped! :)
