# How to multiply 8 and -6 using 2's compliment method?

### 2 respuestas

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• If you are given 8  x (-6) as decimal numbers (ie like in this question) the answer is clearly decimal -48. Then convert 48 to binary and do 2's complement.

If you are given the numbers electronically in binary, like in an ALU, the -6 is already in 2's complement form. Multiplication works directly on 2's complement numbers just the same as with positive numbers. So in this case x8  is achieved by shifting binary -6 left three places and filling with zeros from the right.

• In 2's compliment form, a negative number is the 2's compliment of it's positive number, with the subraction of the two numbers being A - B = A + (2's compliment of B) using much the same method as before, as basically, 2's compliment is 1's compliment + 1.

To get the 2's compliment negative notation of an integer you write out the number in binary .. invert the digits .. and add 1.

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