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Pretest: Rational Expressions and Equations

Select the correct answer.

Which expression is equivalent to [tex]\frac{(x-1)^2}{x^2-x-12} \cdot \frac{x^2+x-6}{x^2-6x+5}[/tex] if no denominator equals zero?

A. [tex]\frac{x^2-3x+2}{x^2-9x+20}[/tex]

B. [tex]\frac{x^2+x-2}{x^2-x-20}[/tex]

C. [tex]\frac{x^2-3x+2}{x^2-x-20}[/tex]

D. [tex]\frac{x^2+3x+2}{x^2+x-20}[/tex]


Sagot :

To solve the given problem and find an equivalent expression for [tex]\(\frac{(x-1)^2}{x^2-x-12} \cdot \frac{x^2+x-6}{x^2-6x+5}\)[/tex], let's go through the steps in detail.

### Step 1: Factorize the Denominators

First, factorize the denominators of the expressions:

- [tex]\(x^2 - x - 12\)[/tex] can be factorized as [tex]\((x - 4)(x + 3)\)[/tex]:
[tex]\[x^2 - x - 12 = (x - 4)(x + 3)\][/tex]

- [tex]\(x^2 - 6x + 5\)[/tex] can be factorized as [tex]\((x - 1)(x - 5)\)[/tex]:
[tex]\[x^2 - 6x + 5 = (x - 1)(x - 5)\][/tex]

### Step 2: Substitute the Factored Forms

Substitute the factored forms into the rational expressions:

[tex]\[ \frac{(x-1)^2}{x^2-x-12} \cdot \frac{x^2 + x - 6}{x^2 - 6x + 5} = \frac{(x-1)^2}{(x-4)(x+3)} \cdot \frac{x^2 + x - 6}{(x-1)(x-5)} \][/tex]

### Step 3: Factor the Numerators

Next, we factorize the numerators if possible:

- [tex]\((x - 1)^2\)[/tex] is already factored.

- [tex]\(x^2 + x - 6\)[/tex] can be factorized as [tex]\((x - 2)(x + 3)\)[/tex]:
[tex]\[x^2 + x - 6 = (x - 2)(x + 3)\][/tex]

### Step 4: Substitute the Factored Numerators

Now, substitute the factored numerators back into the expression:

[tex]\[ \frac{(x-1)^2}{(x-4)(x+3)} \cdot \frac{(x-2)(x+3)}{(x-1)(x-5)} \][/tex]

### Step 5: Simplify the Expression

Combine the expressions and cancel out the common factors:

[tex]\[ \frac{(x-1)^2 (x-2)(x+3)}{(x-4)(x+3)(x-1)(x-5)} \][/tex]

Notice that [tex]\((x-1)\)[/tex] and [tex]\((x+3)\)[/tex] are common factors in the numerator and denominator:

[tex]\[ = \frac{(x-1) (x-2)}{(x-4)(x-5)} \][/tex]

Therefore, the simplified form of the rational expression is:

[tex]\[ \frac{(x-2)(x-1)}{(x-4)(x-5)} \][/tex]

Match this final expression with the options given:

[tex]\[ \frac{(x-2)(x-1)}{(x-4)(x-5)} = \frac{(x - 2)(x - 1)}{(x - 4)(x - 5)} \][/tex]

Which corresponds to Option A, since:

[tex]\[ \boxed{\frac{x^2-3 x+2}{x^2-9 x+20}} \][/tex]

is the same as:

[tex]\[ \frac{(x - 2)(x - 1)}{(x - 4)(x - 5)} \][/tex]

Thus, the correct answer is:

A. [tex]\(\frac{x^2-3 x+2}{x^2-9 x+20}\)[/tex]