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junior college 1 | H2 Maths
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Candice lim
Candice Lim

junior college 1 chevron_right H2 Maths chevron_right Singapore

Hi, could you kindly advise how to find the range of gf(x)? Thank you so much.

Date Posted: 2 years ago
Views: 596
Eric Nicholas K
Eric Nicholas K
2 years ago
Good evening Candice! I will look at this later when I am ready
Candice lim
Candice Lim
2 years ago
Sure sure. Thanks Mr Eric :)
Eric Nicholas K
Eric Nicholas K
2 years ago
Candice, it is noteworthy to know that the range of gf(x) will be equal to the range of g(x) given its input (which is going to come from the output of f(x)).

We say that Rgf = Rg.

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As long as the output of f(x) is a subset of (i.e. is fully contained in) the list of possible inputs of g(x), the composite function will exist.

We say that Rf ⊆ Dg.

Note that every value of the range of f must also be present in the domain of g (hence, the "subset" stipulation).

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In this particular case, our approach is to first find the range (output) of f(x), which upon closer inspection will be all possible outputs except for y = -1.

Since g(x) is generous enough to allow any value of x into it (shown as x ϵ R), it's pretty obvious that the range of f(x) is going to be a (proper) subset of the domain (input) of g(x). So, the composite function gf(x) exists.

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The range of f(x) (all values except for -1) will enter the function g(x) as a domain.

Whatever comes out of g(x) as the output from this input will become its domain, which we can easily work out to be all values except for 3.

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
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Good evening Candice! Here are my workings for this question.
Candice lim
Candice Lim
2 years ago
Good morning Mr Eric,
Thank you so much for explaining to me the working solution. Really appreciated your help!

I hope you have a great day ahead.
Take care :)