Title. I know it goes like that, but as an non mathematician can’t explain it to him.
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You owe me $2, you have -$2.
I take away the $2 you owe me, you have $2 more dollars now.
– signs do the “opposite” of + signs. If 5 + (-2) = 5 – 2 then 5 – (-2) = 5 + 2.
Try arrows? Numbers are an arrow from 0 to the number. Arrows for positive numbers go to the right, arrows for negative numbers go to the left. To add numbers you attach the 2nd arrow to the tip of the first. To subtract, you first flip the 2nd arrow around.
The number line.
0 in the middle with minus numbers on the left and positive numbers on the right.
We always go from zero and to the right, addition, unless told otherwise.
a minus symbol means “move in the opposite direction” i.e. move left
when there is another minus symbol following that still means “move in the opposite direction” i.e. move to the right.
So you start at 4.
Then there is a minus sign saying “move in the opposite direction” I.e. to the left.
You then arrive at another minus sign which says “move in the opposite direction” i.e. to the right (you were moving left with the first minus)
The title is more of an example. Good answers, but I should’ve elaborated my problem.
I’m a teacher and me and my student know that -(-) is a +. But he stubbornly wants to know why that is so. I can give him the examples and he somewhat buys them, but is there some (eli5) mathematical reasoning that I can give him?
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