What is negative 9 times negative 72? (-9 x -72)

What is negative 9 times negative 72?

9 times 72 is 648, but what is the answer if both 9 and 72 are negative numbers? Here we will determine if the answer to negative 9 times negative 72 is positive 648 or negative 648.

There are many different ways to explain and determine if the answer to negative 9 times negative 72 is -648 or +648 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 -648 is the correct answer using basic algebra.

We will test if -648 is correct by setting up the equation negative 9 times negative 72 equals negative 648, and then simplifying the equation to see if it is true.

(-9) (-72) = (-648)

Divide both sides of the equation by (-72) :

		(-9) (-72)
		(-72)

		(-648)
		(-72)

The numerator and denominator on the left side both have (-72) which even each other out and can be removed:

(-9) =

		(-648)
		(-72)

The numerator and denominator on the right side both have a minus sign (-) which even each other out and can be removed:

(-9) =

		(648)
		(72)

A numerator of 648 and denominator of 72 on the right side is the same as 648 divided by 72 which is 9. Now we end up with this untrue equation:

(-9) = (9)

-9 is NOT equal to 9, thus we have proven that negative 9 times negative 72 is not equal to -648. The answer must therefore be 648:

-9 x -72 = 648

The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 9 times negative 72 will always have a positive answer.

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