Expert: Paul Klarreich - 11/23/2009

Question
When two positive or negative directed numbers are multiplied then answer is positive, e.g
(+3)x(+7) = +21 and (-3)x(-7) = +21
What is logic behind it? or what is another way of describibg it?

Also when two numbers of different signs are multiplied then answer is a negative number. e.g.

(+3)x(-7) = -21

How......???????

Please explain

Answer
Questioner:    Rashid
Question: When two positive or negative directed numbers are multiplied then answer is positive, e.g
(+3)x(+7) = +21 and (-3)x(-7) = +21
What is logic behind it? or what is another way of describibg it?

Also when two numbers of different signs are multiplied then answer is a negative number. e.g.

(+3)x(-7) = -21

How......???????

Please explain
.................................
Multiplication is repeated addition.

3*(-8) MEANS  write three  -8's and add them.

That takes care of one question.   Then:

-3 * (anything) means:

- (3 * (anything)), which means

THEOPPOSITEOFTHERESULTOF (3 * (anything))  << you supply the spaces

That should do it.  Think about it for a bit.  Then ask your teacher some more.