What does := mean?

What does := mean?

Answer

It is borrowed from computer programming: it means that the item on the left hand side is being defined to be what is on the right hand side. For example,
y:=7x+2
means that y is defined to be 7x+2.

This is different from, say, writing
1=sin2(θ)+cos2(θ)
where we are saying that the two sides are equal, but we are not defining “1” to be the expression “sin2(θ)+cos2(θ)“.

Basically, some people think that there should be notational difference between saying “I define blah to be equal to blankety” and saying “blah is equal to blankety“. So they use := for the first and = for the latter. Usually, it is clear from context which of the two uses of the equal sign is intended (often because of signal words like “Let”, “We define”, etc.)

Attribution
Source : Link , Question Author : ilhan , Answer Author : Arturo Magidin

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