In my textbook it says that in composition of functions we require domain of second function to be EQUAL to the range of the first. My question is that why cannot the range of the first function be a subset of the domain of the second?

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- Apr 7th 2012, 11:52 PMclerkComposition of function
In my textbook it says that in composition of functions we require domain of second function to be EQUAL to the range of the first. My question is that why cannot the range of the first function be a subset of the domain of the second?

- Apr 8th 2012, 12:43 AMprincepsRe: Composition of function
- Apr 8th 2012, 12:51 AMbiffboyRe: Composition of function
Think about the domain and range of fg and then of the domain and range of the inverse of fg

- Apr 8th 2012, 05:26 AMclerkRe: Composition of function
- Apr 8th 2012, 06:09 AMbiffboyRe: Composition of function
I understand your point. However since the fg means apply g first and then apply f to the answer, the domain of fg cannot include values that were not in the domain of g. The domain of f could have been 'wider' than that of g but the domain of fg would still be restricted to being the same as that of g.

Example g(x)=square root of x Domain: all x > or= to 0

f(x)=x^2 Domain: all real x

fg(x)=x Domain: all x > or= to 0 - Apr 8th 2012, 12:23 PMSylvia104Re: Composition of functions
- Apr 8th 2012, 01:35 PMemakarovRe: Composition of function
Wikipedia says that "range" is sometimes used to mean "codomain." Either the textbook does this, or it unnecessarily restricts the concept of composition.