Success GED Multiplying with Negative numbers
Watch the Khan Academy Video below
The Multiplication Rules:
Positive times a positive = Positive
Negative times a negative = Positive
Positive times a negative = Negative
Negative times a Positive = Negative
Theory , Examples
+ x + = +, +5 x +2 = +10
- x - = +, -5 x -2 = +10
+ x - = -, +5 x -2 = -10
- x + = -, -5 x +2 = -10
Why is negative times a negative a positive?
-1 x +2 = -2 (Negative means, "No, you have to change!" The negative sign is very negative!)
-1 x -2 = +2 (Because the negative sign of the -1 forcing the -2 to change signs. Bossy!)
Lets get deeper...
-1 x -2 x -3 = ??
Okay, first things first: Take -1 x -2 first. We know that negative is going to make the -2 positive, so -1 x -2 = +2.
Take the +2 x -3. The rule is positive is cool if you keep your sign. So +2 x -3 = -6. So -1 x -2 x -3 = -6.
So the more useful rule is that if there are an odd number of negative numbers you're multiplying, the answer will be negative. If there are an even number, the answer will be positive.
