91 times 9 is 819, but what is the answer if both 91 and 9 are negative numbers? Here we will determine if the answer to negative 91 times negative 9 is positive 819 or negative 819.
There are many different ways to explain and determine if the answer to negative 91 times negative 9 is -819 or +819 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 -819 is the correct answer using basic algebra.
We will test if -819 is correct by setting up the equation negative 91 times negative 9 equals negative 819, and then simplifying the equation to see if it is true.
(-91) (-9) = (-819)
Divide both sides of the equation by (-9) :
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| = |
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The numerator and denominator on the left side both have (-9) which even each other out and can be removed:
| (-91) = |
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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:
| (-91) = |
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A numerator of 819 and denominator of 9 on the right side is the same as 819 divided by 9 which is 91. Now we end up with this untrue equation:
(-91) = (91)
-91 is NOT equal to 91, thus we have proven that negative 91 times negative 9 is not equal to -819. The answer must therefore be 819:
-91 x -9 = 819
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 91 times negative 9 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 91 times negative 10?
Here is the next problem on our list that we have explained and calculated.
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