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Which expression is equivalent to [tex]\frac{x+3}{x^2-2x-3} \div \frac{x^2+2x-3}{x+1}[/tex] if no denominator equals zero?

A. [tex]\frac{1}{x^2-2x-3}[/tex]

B. [tex]\frac{1}{x^2-4x+3}[/tex]

C. [tex]\frac{1}{x^2+2x-3}[/tex]

D. [tex]\frac{x+3}{x+1}[/tex]


Sagot :

To determine which expression is equivalent to [tex]\(\frac{x+3}{x^2 - 2x - 3} \div \frac{x^2 + 2x - 3}{x + 1}\)[/tex], we need to follow these steps:

### Step 1: Simplify the Division of Fractions
Recall that dividing by a fraction is equivalent to multiplying by its reciprocal. Thus the given expression can be rewritten as:
[tex]\[ \frac{x+3}{x^2 - 2x - 3} \div \frac{x^2 + 2x - 3}{x+1} = \frac{x+3}{x^2 - 2x - 3} \times \frac{x+1}{x^2 + 2x - 3} \][/tex]

### Step 2: Examine the Numerator and Denominator
We have two parts to consider now:
1. [tex]\(\frac{x + 3}{x^2 - 2x - 3}\)[/tex]
2. [tex]\(\frac{x + 1}{x^2 + 2x - 3}\)[/tex]

### Step 3: Factorize the Denominators
To make our simplifications easier, we factorize the denominators.

For [tex]\(x^2 - 2x - 3\)[/tex]:
[tex]\[ x^2 - 2x - 3 = (x - 3)(x + 1) \][/tex]

For [tex]\(x^2 + 2x - 3\)[/tex]:
[tex]\[ x^2 + 2x - 3 = (x + 3)(x - 1) \][/tex]

### Step 4: Substitute the Factored Forms
Replace the factored forms in our original expression:
[tex]\[ \frac{x + 3}{(x - 3)(x + 1)} \times \frac{x + 1}{(x + 3)(x - 1)} \][/tex]

### Step 5: Simplify the Expression
Now, simplify the expression by canceling common terms:
[tex]\[ \frac{x + 3}{(x - 3)(x + 1)} \times \frac{x + 1}{(x + 3)(x - 1)} = \frac{(x + 3) \cdot (x + 1)}{(x - 3)(x + 1) \cdot (x + 3)(x - 1)} \][/tex]
[tex]\[ = \frac{1}{(x - 3)(x - 1)} \][/tex]

### Step 6: Determine the Equivalent Expression
Now, we compare our simplified expression [tex]\(\frac{1}{(x - 3)(x - 1)}\)[/tex] with the given answer choices:

[tex]\[ (x - 3)(x - 1) = x^2 - 4x + 3 \][/tex]

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

Thus, the answer choice that matches [tex]\(\frac{1}{x^2 - 4x + 3}\)[/tex] is:

### Final Answer
[tex]\[ \boxed{B} \][/tex]
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