90 times 9 is 810, but what is the answer if both 90 and 9 are negative numbers? Here we will determine if the answer to negative 90 times negative 9 is positive 810 or negative 810.
There are many different ways to explain and determine if the answer to negative 90 times negative 9 is -810 or +810 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 -810 is the correct answer using basic algebra.
We will test if -810 is correct by setting up the equation negative 90 times negative 9 equals negative 810, and then simplifying the equation to see if it is true.
(-90) (-9) = (-810)
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:
| (-90) = |
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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:
| (-90) = |
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A numerator of 810 and denominator of 9 on the right side is the same as 810 divided by 9 which is 90. Now we end up with this untrue equation:
(-90) = (90)
-90 is NOT equal to 90, thus we have proven that negative 90 times negative 9 is not equal to -810. The answer must therefore be 810:
-90 x -9 = 810
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 90 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 90 times negative 10?
Here is the next problem on our list that we have explained and calculated.
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