Chapter 0.2, Problem 63E

a.

To determine

To graph: $\left(f\circ g\right)\left(x\right),\left(g\circ f\right)\left(x\right)$ ,where $f\left(x\right)=x-7,g\left(x\right)=\sqrt{x}$ and then write a conjecture about domain and range of each function.

Explanation of Solution

Given information:

The given function are $f\left(x\right)=x-7,g\left(x\right)=\sqrt{x}$

Concept used:

The composition $f\text{of}\text{g}\text{of}\text{x}$ is the composition $f$ with $g$ .The value of $f^{o}g\left(x\right)=f\left(g\left(x\right)\right)$ .

Calculations:

  $g\left(x\right)=\sqrt{x}$

Replace $x$ by $g\left(x\right)=\sqrt{x}$ in $f\left(x\right)$ to get $f\left(g\left(x\right)\right)$ .

  $\begin{array}{c}\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)\\ f\left(g\left(x\right)\right)=f\left(\sqrt{x}\right)\\ =\sqrt{x}-7\\ \left(g\circ f\right)\left(x\right)=g\left(f\left(x\right)\right)\\ =g\left(x-7\right)\\ =\sqrt{x-7}\end{array}$

The graph of $\left(f\circ g\right)\left(x\right)=\sqrt{x}-7$ is given below.

  

The graph of $\left(g\circ f\right)\left(x\right)=\sqrt{x-7}$ is given below

  

Conjecture:

The domain of the composite function $\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)$ the set of input value for in the domain $g\left(x\right)$ for which $g\left(x\right)$ is the domain of $f\left(x\right)$ in $\left(f\circ g\right)$ and the range is depend on the newly formed composition function.

Similarly the domain of the composite function $\left(g\circ f\right)\left(x\right)=g\left(f\left(x\right)\right)$ the set of input value for in the domain $f\left(x\right)$ in which $f\left(x\right)$ is the domain of $g\left(x\right)$ in $g\circ f\left(x\right)$ and the range is depend on the newly formed composition function.

b.

To determine

To find : Domain and range of $\left(f\circ g\right)\left(x\right),\left(g\circ f\right)\left(x\right)$ , using conjecture where $f\left(x\right)=x-7,g\left(x\right)=\sqrt{x}$ ..

Explanation of Solution

Given information:

The given function are $f\left(x\right)=x-7,g\left(x\right)=\sqrt{x}$

Concept used:

The composition $f\text{of}\text{g}\text{of}\text{x}$ is the composition $f$ with $g$ .The value of $\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)$ .

The domain of the composite function $\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)$ the set of input value for in the domain $g\left(x\right)$ for which $g\left(x\right)$ is the domain of $f\left(x\right)$ in $\left(f\circ g\right)\left(x\right)$ and the range is not depend on the inner function .

Similarly the domain of the composite function $\left(g\circ f\right)\left(x\right)=g\left(f\left(x\right)\right)$ the set of input value for in the domain $f\left(x\right)$ in which $f\left(x\right)$ is the domain of $g\left(x\right)$ in $g\circ f\left(x\right)$ and the range is not depend on the inner function.

Calculations:

Here $g\left(x\right)=\sqrt{x}$

The domain of $g\left(x\right)$ is $x\in R,x\ge 0.$

The domain of $f\left(x\right)=x-7$ , is any real valued function.

Then domain of $\left(f\circ g\right)\left(x\right)=\sqrt{x}-7$ is $x\in R,x\ge 0.$

Based on the conjecture domain depends on inner and outer function .

The range of the composite function $\left(f\circ g\right)\left(x\right)=\sqrt{x}-7$ is $y\ge -7$ .

The domain of $\left(g\circ f\right)\left(x\right)=\sqrt{x-7}$ is $x\ge 7$ since here inner function is $f\left(x\right)=x-7$ so domain of $\left(g\circ f\right)\left(x\right)$ will depend on inner function.

And the range will be $y\ge 0$ .