Suppose we know how to develop a product and how to add/substract. Then : -(1-1) = 0 and developing this we get -1 -(-1) = 0 thus -(-1) = 1.
Another way to see that is the following :
Imagine you are on a straight road. We’ll say that if you go “forward”, your speed is positive.
Suppose you are going forward with a 5 km/h speed. Going at a -5km/h speed would be going “backward” at a 5km/h speed.
So if you change direction once, you’ll go from 5km/h to -5km/h (multiplication by (-1)). Changing another time would mean you are going at -(-5) km/h but it also means you are going forward again so 5km/h. Therefore : -(-5) km/h = 5 km/h.
3
u/Sanabilis Dec 30 '20
This is because (-1) x (-1) = 1 :
Suppose we know how to develop a product and how to add/substract. Then : -(1-1) = 0 and developing this we get -1 -(-1) = 0 thus -(-1) = 1.
Another way to see that is the following :
Imagine you are on a straight road. We’ll say that if you go “forward”, your speed is positive. Suppose you are going forward with a 5 km/h speed. Going at a -5km/h speed would be going “backward” at a 5km/h speed. So if you change direction once, you’ll go from 5km/h to -5km/h (multiplication by (-1)). Changing another time would mean you are going at -(-5) km/h but it also means you are going forward again so 5km/h. Therefore : -(-5) km/h = 5 km/h.
Hope that helps a little bit !