78 times 8 is 624, but what is the answer if both 78 and 8 are negative numbers? Here we will determine if the answer to negative 78 times negative 8 is positive 624 or negative 624.
There are many different ways to explain and determine if the answer to negative 78 times negative 8 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 78 times negative 8 equals negative 624, and then simplifying the equation to see if it is true.
(-78) (-8) = (-624)
Divide both sides of the equation by (-8) :
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| = |
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The numerator and denominator on the left side both have (-8) which even each other out and can be removed:
| (-78) = |
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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:
| (-78) = |
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A numerator of 624 and denominator of 8 on the right side is the same as 624 divided by 8 which is 78. Now we end up with this untrue equation:
(-78) = (78)
-78 is NOT equal to 78, thus we have proven that negative 78 times negative 8 is not equal to -624. The answer must therefore be 624:
-78 x -8 = 624
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 78 times negative 8 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 78 times negative 9?
Here is the next problem on our list that we have explained and calculated.
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