Math Is Fun Forum

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Little question

Hi, : http://imageshack.us/photo/my-images/827/34f2.png/

I'm just wondering, I know that a rational expression can't be divided by 0, but what does he man by "identically" ???I feel like there's something I'm missing... any help please ! Thank you !

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Little question

x-x is identically equal to 0 because it is 0 for any value of x.

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: Little question

hi Al-Allo

In your example you could drop the word altogether and have "The only restriction is that the divisor must not be equal to zero"  and it still makes perfect sense.  I've been trying to find situations where just using 'equals' is not appropriate ...  without much success I have to say.

Some mathematicians use 'identically equal' instead of 'equivalent' and it is often used for identities eg.

and also eg.

If you google the two word phrase you'll get more examples.

Meanwhile, here's a challenge for members:

Find an example where you cannot leave out the word 'identically' without changing the meaning. 

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Re: Little question

Ok, thank you.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Little question

Hi Bob

In math or in general?

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: Little question

hi Stefy,

I'm be interested in either / both.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Little question

In math such an example, I think, doesn't exist. But, either way, the question is a bit ambiguous.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: Little question

I suppose what I'm really saying is the word 'identically'  is redundant in the sentence.  So then I wonder, is it always redundant.  So far, I think, yes.  So I'm curious about whether a case exists where it isn't.

I prefer concepts to words in maths.  There are often many ways of expressing the same idea.  Sometimes posters get hung up on the words when I think they should be concentrating on the concepts.  The same is true of the symbols used.  eg. the recent Boolean algebra question.  There are at least three different notations there, but the underlying maths is consistent throughout.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob