Division by zero

1. Jan 26, 2007

Ahmed Ismail

Goodmorning all
I want to know why 0 divide anything = zero, and why division by zero is undefined?

regards

2. Jan 26, 2007

HallsofIvy

Saying a/b= c means that a= bc. If a/0= c then a= 0c. But 0 times any number is 0- the equation a= 0c for a not equal to 0 is impossible so a/0= c is also impossible. If a= 0, theres a different problem. 0/0= c becomes 0= 0c which true no matter what c is! We still are unable to say that 0/c is any particular number.

Many math textbooks use the term "undefined" for a/0 when a is not zero and "undetermined" for 0/0 because of that difference.

3. Jan 26, 2007

arildno

1. There is no such SEPARATE thing called "division" as you've learnt it(contrary to school teaching).
What you DO have, is the following:
Given any non-zero real number "a", there exists another number, that we have given the name "(1/a)", that has the property when multiplied with "a" yields the number 1, that is: a*(1/a)=1.
We can prove that for any particular number "a", the number "(1/a)" is UNIQUE, so the identity a*(1/a)=1 can be said to DEFINE (1/a) (just like we DEFINE "2" to be the number so that 1+1=2, really)

Whenever we multiply (1/a) with some other number, say b, that is we form the product b*(1/a), we find this notation so cumbersome so that in short hand, we introduce the notation b/a=b*(1/a).

Now, we can prove that whenever we multiply a number with 0, then we get 0, so for any "a", we have 0/a=0*(1/a)=0, providing the answer to your first question.

The answer to your second question is also contained here, because if 0*anything=0, then, since 1 isn't 0, then there CAN'T exist a number (1/0) having the property 0*(1/0)=1 (remember I required that a had to be non-zero earlier?)
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