1 times 9 is 9, but what is the answer if both 1 and 9 are negative numbers? Here we will determine if the answer to negative 1 times negative 9 is positive 9 or negative 9.
There are many different ways to explain and determine if the answer to negative 1 times negative 9 is -9 or +9 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 -9 is the correct answer using basic algebra.
We will test if -9 is correct by setting up the equation negative 1 times negative 9 equals negative 9, and then simplifying the equation to see if it is true.
(-1) (-9) = (-9)
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:
| (-1) = |
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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:
| (-1) = |
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A numerator of 9 and denominator of 9 on the right side is the same as 9 divided by 9 which is 1. Now we end up with this untrue equation:
(-1) = (1)
-1 is NOT equal to 1, thus we have proven that negative 1 times negative 9 is not equal to -9. The answer must therefore be 9:
-1 x -9 = 9
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 1 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 1 times negative 10?
Here is the next problem on our list that we have explained and calculated.
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