Question

Why, if two wrongs don't make a right, do two negatives make a positive in Mathematics .​

Answer 1

think you may be trying to mix the worlds of morals and mathematics, which doesn’t really work. You also need to take magnitude into account.

If you break my window and then I go and break yours, it might temporarily make me feel better, in a childish way, but the world is hardly better for two broken windows rather than one, though some people might see that as reasonable. If I escalate this and, say, set fire you your car in retaliation, we may well wonder where this will all end. Wars have started from such small incidents.

Mathematics is much more precise. If I owe you fifty dollars then I’m in debt; effectively I have a negative amount of money.

But if someone else also owes me sixty dollars then I notionally have ten dollars and I’m not in debt. If I’m only owed forty dollars I still have a ten dollar debt, or if I’m owed fifty it’s zero.

in short word

When you multiply a negative by a negative you get a positive, because the two negative signs are cancelled out.