Chapter 1.5, Problem 47E

(a)

To determine

To calculate: To determine domain of $f$

Answer to Problem 47E

Domain of f is set of all real numbers

Explanation of Solution

Given:

  $f(x)=x^2+1$

Formula Used:

The domain of a function is the set of its possible inputs, i.e., the set of input values where for which the function is defined.

Calculation:

Domain of $f$ is calculated as:

Given $f(x)=x^2+1$

Now clearly, $f(x)$ is defined for all values of x

Therefore, domain of f is set of all real numbers.

Conclusion:

Hence, domain of f is set of all real numbers.

(b)

To determine

To calculate: To determine domain of $g$

Answer to Problem 47E

Domain of g is set of all real numbers such that

  $x\ge 0$

Explanation of Solution

Given:

  $g(x)=\sqrt{x}$

Formula Used:

The domain of a function is the set of its possible inputs, i.e., the set of input values where for which the function is defined.

Calculation:

Domain of $g$ is calculated as:

Given $g(x)=\sqrt{x}$

For $g(x)$ to be defined,

  $x\ge 0$

Therefore, domain of g is set of all real numbers such that

  $x\ge 0$

Conclusion:

Hence domain of g is set of all real numbers such that

  $x\ge 0$

(c)

To determine

To calculate: To determine domain of $f\circ g$

Answer to Problem 47E

Domain of $f\circ g$ is set of all real numbers such that $x\ge 0$

Explanation of Solution

Given:

  $f(x)=x^2+1$

  $g(x)=\sqrt{x}$

Formula Used:

1. Composition of functions is when one function is inside of another function.

The notation used for the composition of functions looks like this, $\left(f\circ g\right)\left(x\right)$ .

The composition of the function f with g is defined as follows:

  $\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)$ , notice that in the case the function g is inside of the function

2. The domain of a function is the set of its possible inputs, i.e., the set of input values where for which the function is defined.

Calculation:

  $f\circ g$ is calculated as:

  $\left(f\circ g\right)\left(x\right)=f\left(g\left(x\right)\right)$

Substitute: $g(x)=\sqrt{x}$

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

Also, given $f(x)=x^2+1$

Thus, $\left(f\circ g\right)\left(x\right)$ is calculated as

  $\begin{array}{l}\left(f\circ g\right)\left(x\right)=\left(\sqrt{x}\right)+1\\ \left(f\circ g\right)\left(x\right)=x+1\end{array}$

Above function “ x +1” is defined for all values of x

From Part a: Domain of f is set of all real numbers

From Part b: Domain of g is set of all real numbers such that

  $x\ge 0$

Therefore, Domain of $f\circ g$ is set of all real numbers such that $x\ge 0$

Conclusion:

Hence, domain of $f\circ g$ is set of all real numbers such that $x\ge 0$