31.03 - The sum and difference

The sum of two numbers

Adding two numbers together is called the sum. The sum is usually mathematically denoted as a plus symbol: $+$

The two numbers used in the sum are called the terms.

For example:

• The sum of 2 and 6 is: $2+6$
  • 2 and 6 are the terms
• The sum of 1 and 3 is: $1+3$
  • 1 and 3 are the terms
• The sum of 3 and 4 is: $3+4$
  • 3 and 4 are the terms

The difference of two numbers

Subtracting two numbers from each other is called the difference.

The difference is usually mathematically denoted as a minus symbol: $-$

The two numbers used in the sum are called the terms.

For example:

• The difference between 6 and 2 is: $6-2$
  • 6 and 2 are the terms
• The difference between 5 and 3 is: $5-3$
  • 5 and 3 are the terms
• The difference between 7 and 4 is: $7-4$
  • 7 and 4 are the terms

The sum, difference, and negatives

Negative numbers can change a sum into a difference and vice versa. Take the following equation for example:
$5+-3$

$-3$ will be added to $5$. This really just means that $3$ will be subtracted from $5$, since adding a negative number will do the opposite.
So you could also write:
$5-3$

Let’s take another example:
$-5--3$

$-3$ will be subtracted from $-5$. Once again, this will turn to the opposite and $3$ will be added to $-5$:
$-5+3$

This might seem confusing so let me explain.
A good trick to figure out whether plus or minus will turn out on top is to:

• read $+$ as yes
• read $-$ as not.
• $++$ will be yes yes, which is the same as saying yes ($+$)
• $+-$ will be yes not, which is the same as saying not ($-$)
• $-+$ will be not yes, which is the same as saying not ($-$)
• $--$ will be not not, which is the same as saying yes ($+$)

As you can see, the first operator will decide if its either plus or minus, the second operator will decide whether the outcome will flip around or not.
a plus($+$) will keep it the same and a minus($-$) will flip it.

Keep in mind that the second operator isnt actually an operator

It is an indicator that the number is negative. The dual operator trick i showed is just to make adding/subtracting with negative numbers easier.

next chapter

The next chapter will go over the product