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Multiplication of a Positive and a Negative Integers

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Multiplication of a Positive and a Negative Integer:

We know that the multiplication of whole numbers is repeated addition.
For example, 8 + 8 + 8 = 3 × 8 = 24.

Similarly, the multiplication of integers numbers is repeated addition.

Observe the following examples:
1) We have from the following number line, (– 4) + (– 4) + (– 4) + (– 4) + (– 4) = 5 × (– 4) = – 20.

2) Let us see how to find the product of a positive integer and a negative integer without using the number line.

Let us find 3 × (–5) in a different way.
First, find 3 × 5 and then put minus sign (–) before the product obtained.
You get – 15. That is we find – (3 × 5) to get – 15.

Thus, multiplying a positive integer and a negative integer, we multiply them as whole numbers and put a minus sign (–) before the product. We thus get a negative integer.

In general, for any two positive integers a, and b we can say a × (– b) = (– a) × b = – (a × b).

Example

Multiply.

(-5) × 4

(-5) × 4 = - 20

Example

Multiply.
(-7) × (18)

(-7) × (18) = 126

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