How do you evaluate #(-41)+(-40)#?
2 Answers
Explanation:
When dealing with adding and subtracting negative numbers, a good way to think of it is to picture yourself standing on a number line. To perform the operation of adding
In this example, we've been asked to start at
(Incidentally, you can use this idea to show yourself that adding a negative value is the same as subtracting that positive value.)
Bonus:
If you've heard of (or seen) vectors before, they are another useful way to think about this. Vectors are arrows that have a length and a direction.
---> This vector has a length of 3, and is facing right. It represents +3.
<-- This vector has length 2, but is facing left. It represents -2.
Adding two vectors means taking the 2nd one's tail, and placing it at the 1st one's tip, without changing its direction. (Remember, vectors have a direction, so if we change the direction, we change the vector, and we don't want to do that.) The sum is the vector you get when you start from the 1st tail and go to the 2nd tip.
Suppose we want to add
Simple, right? Now, suppose we want to add
I won't be able to draw vectors with length 40 or 41 here, but hopefully you get the idea. If you like the vector notation, try to use it to explain subtraction.
-81
Explanation:
Add together 2 negative numbers and the answer is negative
Add together 2 positive numbers and the answer is positive
We have the first condition. If you like think of add as 'put together'
So we are putting together
Thus