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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.
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 :)