I don't really understand the fogs & gofs of composite functions – in particular finding the range of a composite function
If anyone would be able to help with the questions below it would be much appreciated!
1) Given the functions f(x) = 1/x and g(x) = x^2 + 1, find the (domain) and range of f(g(x))
- So far I've gotten that the domain of this composite function is R/all real numbers
2) Given the functions f(x) = sin(x), x∈[0, 2pi] and g(x) = x^2 - 4, x∈[-2,2], find the domain and range of g(f(x))
Question 1\[f:\mathbb{R}\setminus\{0\}\to\mathbb{R},\ f(x)=\frac{1}{x}\quad\text{and}\quad g:\mathbb{R}\to\mathbb{R},\ g(x)=x^2+1\]Here, \(\text{range}(g)=[1,\infty)\subseteq \text{domain}(f)=\mathbb{R}\setminus\{0\}\), so \(f(g(x))\) is defined.
As you already said, \(\text{domain}(f\circ g)=\text{domain}(g)=\mathbb{R}\).
Let us just take a step back for a second and think about what we're actually doing here.
We plug in a real number \(x\) into \(g\) and the output is somewhere in \([1,\infty)\). This output of \(g\) then goes in as the input for \(f\).
Essentially: \(\mathbb{R}\overset{g}{\longrightarrow}[1,\infty)\overset{f}{\longrightarrow}\text{range}(f\circ g)\).
In order words, \(\text{range}(f\circ g)=\text{range}(f^*)\), where \[f^*:[1,\infty)\to\mathbb{R},\ f^*(x)=\frac{1}{x}.\] A quick sketch of the graph of \(f^*\) shows that \(\text{range}(f\circ g)=(0,1]\).
Question 2This is the same sort of idea as Question 1. I'll start you off, and I'll leave it with you. \[f:[0,2\pi]\to\mathbb{R},\ f(x)=\sin(x)\quad \text{and}\quad g:[-2,2]\to\mathbb{R},\ g(x)=x^2-4.\] Clearly, \(\text{range}(f)=[-1,1]\subseteq \text{domain}(g)=[-2,2]\), so \(g(f(x))\) is defined.
As before, \(\text{domain}(g\circ f)=\text{domain}(f)=[0,2\pi]\).
In this case: \([0,2\pi]\overset{f}{\longrightarrow}[-1,1]\overset{g}{\longrightarrow}\text{range}(g\circ f)\).
So, what's the range of \(g\circ f\) here?
Edit: S_R_K by milliseconds lol