8 times 78 is 624, but what is the answer if both 8 and 78 are negative numbers? Here we will determine if the answer to negative 8 times negative 78 is positive 624 or negative 624.
There are many different ways to explain and determine if the answer to negative 8 times negative 78 is -624 or +624 using mathematical terms such as additive inverse and mathematical laws like the Distribute Law.
We will take a different approach - process of elimination: We will simply test if -624 is the correct answer using basic algebra.
We will test if -624 is correct by setting up the equation negative 8 times negative 78 equals negative 624, and then simplifying the equation to see if it is true.
(-8) (-78) = (-624)
Divide both sides of the equation by (-78) :
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| = |
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The numerator and denominator on the left side both have (-78) which even each other out and can be removed:
| (-8) = |
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The numerator and denominator on the right side both have a minus sign (-) which even each other out and can be removed:
| (-8) = |
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A numerator of 624 and denominator of 78 on the right side is the same as 624 divided by 78 which is 8. Now we end up with this untrue equation:
(-8) = (8)
-8 is NOT equal to 8, thus we have proven that negative 8 times negative 78 is not equal to -624. The answer must therefore be 624:
-8 x -78 = 624
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 8 times negative 78 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 8 times negative 79?
Here is the next problem on our list that we have explained and calculated.
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