College

The functions [tex]h(x)[/tex] and [tex]l(x)[/tex] are defined by:

[tex]h(x) = \frac{3}{3 - 2x} \quad \text{and} \quad l(x) = \frac{2x}{2x - 3}[/tex].

Suppose the symbols [tex]D_h[/tex] and [tex]D_l[/tex] denote the domains of [tex]h[/tex] and [tex]l[/tex], respectively. Determine and simplify the equation that defines:

1. The domain of [tex]h[/tex] and [tex]l[/tex], respectively, [tex]D_h[/tex] and [tex]D_l[/tex].

2. [tex]h + l[/tex] and give the set [tex]D_{h+l}[/tex].

3. [tex]h - l[/tex] and give the set [tex]D_{h-l}[/tex].

4. [tex]h \cdot l[/tex] and give the set [tex]D_{h \cdot l}[/tex].

5. [tex]\frac{h}{l}[/tex] and give the set [tex]D_q[/tex].

Answer :

We are given the functions

[tex]$$
h(x)=\frac{3}{3-2x} \quad \text{and} \quad l(x)=\frac{2x}{2x-3}.
$$[/tex]

Let us go through the steps to determine the domains and the results for each operation.

─────────────────────────────
Step 1. Determining the Domains of [tex]\(h(x)\)[/tex] and [tex]\(l(x)\)[/tex]

For [tex]\(h(x)=\frac{3}{3-2x}\)[/tex], the denominator must not be zero:

[tex]\[
3-2x \neq 0 \quad\Longrightarrow\quad x \neq \frac{3}{2}.
\][/tex]

Thus, the domain of [tex]\(h\)[/tex] is

[tex]\[
D_h=\{x\in\mathbb{R} : x\neq \frac{3}{2}\}.
\][/tex]

For [tex]\(l(x)=\frac{2x}{2x-3}\)[/tex], we require

[tex]\[
2x-3 \neq 0 \quad\Longrightarrow\quad x\neq \frac{3}{2}.
\][/tex]

So, the domain of [tex]\(l\)[/tex] is

[tex]\[
D_l=\{x\in\mathbb{R} : x\neq \frac{3}{2}\}.
\][/tex]

─────────────────────────────
Step 2. Calculating [tex]\(h(x)+l(x)\)[/tex] and Its Domain

Notice that in [tex]\(l(x)\)[/tex], we have

[tex]\[
2x-3=-(3-2x).
\][/tex]

So, we may rewrite

[tex]\[
l(x) = \frac{2x}{2x-3} = -\frac{2x}{3-2x}.
\][/tex]

Then,

[tex]\[
h(x)+l(x) = \frac{3}{3-2x} - \frac{2x}{3-2x} = \frac{3-2x}{3-2x}.
\][/tex]

For [tex]\(x\neq \frac{3}{2}\)[/tex] (since [tex]\(3-2x\neq 0\)[/tex]), the fraction in the numerator simplifies to

[tex]\[
h(x)+l(x)=1.
\][/tex]

The domain of [tex]\(h+l\)[/tex] is the common domain of [tex]\(h\)[/tex] and [tex]\(l\)[/tex]:

[tex]\[
D_{h+l}=\{x\in\mathbb{R} : x\neq \frac{3}{2}\}.
\][/tex]

─────────────────────────────
Step 3. Calculating [tex]\(h(x)-l(x)\)[/tex] and Its Domain

Using the same rewriting for [tex]\(l(x)\)[/tex]:

[tex]\[
h(x)-l(x)=\frac{3}{3-2x} + \frac{2x}{3-2x} = \frac{3+2x}{3-2x}.
\][/tex]

The domain is again

[tex]\[
D_{h-l}=\{x \in\mathbb{R} : x\neq \frac{3}{2}\}.
\][/tex]

─────────────────────────────
Step 4. Calculating [tex]\(h(x)\cdot l(x)\)[/tex] and Its Domain

Multiplying the two functions we have

[tex]\[
h(x)\cdot l(x)=\frac{3}{3-2x}\cdot \frac{2x}{2x-3}.
\][/tex]

Notice that

[tex]\[
(3-2x)(2x-3) = (3-2x)\Big[-(3-2x)\Big] = -\bigl(3-2x\bigr)^2.
\][/tex]

Thus, we can simplify as follows:

[tex]\[
h(x) \cdot l(x) = \frac{6x}{-(3-2x)^2}=-\frac{6x}{(3-2x)^2}.
\][/tex]

The domain remains the common domain of both functions:

[tex]\[
D_{h\cdot l}=\{x\in\mathbb{R} : x\neq \frac{3}{2}\}.
\][/tex]

─────────────────────────────
Step 5. Calculating [tex]\(\frac{h(x)}{l(x)}\)[/tex] and Its Domain

We have

[tex]\[
\frac{h(x)}{l(x)}=\frac{\frac{3}{3-2x}}{\frac{2x}{2x-3}}=\frac{3}{3-2x}\cdot\frac{2x-3}{2x}.
\][/tex]

Again, using [tex]\(2x-3=-(3-2x)\)[/tex], we get:

[tex]\[
\frac{h(x)}{l(x)}=\frac{3}{3-2x}\cdot\frac{-\left(3-2x\right)}{2x}=-\frac{3}{2x}.
\][/tex]

In addition to the restriction [tex]\(x\neq \frac{3}{2}\)[/tex] (from the domains of [tex]\(h\)[/tex] and [tex]\(l\)[/tex]), we must also avoid values that make the denominator of this final expression zero (i.e. [tex]\(2x\neq 0\)[/tex] or [tex]\(x\neq 0\)[/tex]). Therefore, the domain is

[tex]\[
D_{h/l}=\{x\in\mathbb{R}: x\neq \frac{3}{2} \text{ and } x\neq 0\}.
\][/tex]

─────────────────────────────
Summary of Answers

1. Domains:
- [tex]\( D_h=\{x\in\mathbb{R} : x\neq \frac{3}{2}\} \)[/tex]
- [tex]\( D_l=\{x\in\mathbb{R} : x\neq \frac{3}{2}\} \)[/tex]

2. For [tex]\(h(x)+l(x)\)[/tex]:
- Expression: [tex]\( h(x)+l(x)=1 \)[/tex]
- Domain: [tex]\( D_{h+l}=\{x\in\mathbb{R} : x\neq \frac{3}{2}\} \)[/tex]

3. For [tex]\(h(x)-l(x)\)[/tex]:
- Expression: [tex]\( h(x)-l(x)=\frac{3+2x}{3-2x} \)[/tex]
- Domain: [tex]\( D_{h-l}=\{x\in\mathbb{R} : x\neq \frac{3}{2}\} \)[/tex]

4. For [tex]\(h(x)\cdot l(x)\)[/tex]:
- Expression: [tex]\( h(x)\cdot l(x)=-\frac{6x}{(3-2x)^2} \)[/tex]
- Domain: [tex]\( D_{h\cdot l}=\{x\in\mathbb{R} : x\neq \frac{3}{2}\} \)[/tex]

5. For [tex]\(\frac{h(x)}{l(x)}\)[/tex]:
- Expression: [tex]\( \frac{h(x)}{l(x)}=-\frac{3}{2x} \)[/tex]
- Domain: [tex]\( D_{h/l}=\{x\in\mathbb{R} : x\neq \frac{3}{2} \text{ and } x\neq 0\} \)[/tex]

Each step carefully considers the conditions under which the original functions and their combinations are defined.