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junior college 1 | H2 Maths
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Hi, could you kindly advise how to find the range of gf(x)? Thank you so much.
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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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 :)