87 times 15 is 1305, but what is the answer if both 87 and 15 are negative numbers? Here we will determine if the answer to negative 87 times negative 15 is positive 1305 or negative 1305.
There are many different ways to explain and determine if the answer to negative 87 times negative 15 is -1305 or +1305 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 -1305 is the correct answer using basic algebra.
We will test if -1305 is correct by setting up the equation negative 87 times negative 15 equals negative 1305, and then simplifying the equation to see if it is true.
(-87) (-15) = (-1305)
Divide both sides of the equation by (-15) :
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| = |
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The numerator and denominator on the left side both have (-15) which even each other out and can be removed:
| (-87) = |
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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:
| (-87) = |
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A numerator of 1305 and denominator of 15 on the right side is the same as 1305 divided by 15 which is 87. Now we end up with this untrue equation:
(-87) = (87)
-87 is NOT equal to 87, thus we have proven that negative 87 times negative 15 is not equal to -1305. The answer must therefore be 1305:
-87 x -15 = 1305
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 87 times negative 15 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
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