7 times 13 is 91, but what is the answer if both 7 and 13 are negative numbers? Here we will determine if the answer to negative 7 times negative 13 is positive 91 or negative 91.
There are many different ways to explain and determine if the answer to negative 7 times negative 13 is -91 or +91 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 -91 is the correct answer using basic algebra.
We will test if -91 is correct by setting up the equation negative 7 times negative 13 equals negative 91, and then simplifying the equation to see if it is true.
(-7) (-13) = (-91)
Divide both sides of the equation by (-13) :
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| = |
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The numerator and denominator on the left side both have (-13) which even each other out and can be removed:
| (-7) = |
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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:
| (-7) = |
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A numerator of 91 and denominator of 13 on the right side is the same as 91 divided by 13 which is 7. Now we end up with this untrue equation:
(-7) = (7)
-7 is NOT equal to 7, thus we have proven that negative 7 times negative 13 is not equal to -91. The answer must therefore be 91:
-7 x -13 = 91
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 7 times negative 13 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 7 times negative 14?
Here is the next problem on our list that we have explained and calculated.
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