Math Is Fun Forum

Onyx

Member

Registered: 2009-02-24

Posts: 48

relation :=

Recently I keep seeing this symbol used everywhere, :=, and at first I thought it was a typo, but I've seen it numerous times in different texts. What's the difference between this and the simple equals sign?

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: relation :=

This is exactly the same as an equals sign, but used when defining something new.
As an example, if I'm solving a question involving functions f and g, I might say:

"Now we introduce a new function h, where h(x) = f(x) - g(x)."

But that's far too long a sentence for us lazy mathematicians, so instead I say:
"Now consider h := f - g."

I could have also said f - g =: h if I'd wanted.

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Why did the vector cross the road?
It wanted to be normal.

Onyx

Member

Registered: 2009-02-24

Posts: 48

Re: relation :=

Thanks