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Select the correct answer.

The domain of the function [tex]\( f \)[/tex] is [tex]\((-\infty, \infty)\)[/tex]. The value of the function approaches [tex]\(-\infty\)[/tex] as [tex]\( x \)[/tex] approaches [tex]\(-\infty\)[/tex], and the value of the function approaches [tex]\(\infty\)[/tex] as [tex]\( x \)[/tex] approaches [tex]\(\infty\)[/tex]. Which function could be [tex]\( f \)[/tex]?

A. [tex]\( f(x) = \frac{x^2 - 36}{x - 6} \)[/tex]
B. [tex]\( f(x) = \frac{x - 6}{x^2 - 3} \)[/tex]
C. [tex]\( f(x) = \frac{x + 6}{x - 6} \)[/tex]
D. [tex]\( f(x) = \frac{x - 6}{x + 6} \)[/tex]


Sagot :

To determine the function [tex]\(\cap\)[/tex] that matches the criteria provided in the question, let us analyze each of the given function options (A, B, C, and D) by evaluating their limits as [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex] and [tex]\(-\infty\)[/tex].

### Option A: [tex]\(f(x) = \frac{x^2 - 36}{x - 6}\)[/tex]

1. Limit as [tex]\(x \to \infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex], the numerator [tex]\(x^2 - 36\)[/tex] grows much faster than the denominator [tex]\(x - 6\)[/tex].
- Therefore, the value of [tex]\(f(x)\)[/tex] tends to [tex]\(\infty\)[/tex].

2. Limit as [tex]\(x \to -\infty\)[/tex]:
- Similarly, as [tex]\(x\)[/tex] approaches [tex]\(-\infty\)[/tex], the numerator [tex]\(x^2 - 36\)[/tex] remains positive and grows faster than the linear denominator [tex]\(x - 6\)[/tex].
- Thus, the value of [tex]\(f(x)\)[/tex] tends to [tex]\(\infty\)[/tex].

Since the value approaches [tex]\(\infty\)[/tex] in both directions, this does not match the criteria.

### Option B: [tex]\(f(x) = \frac{x - 6}{x^2 - 3}\)[/tex]

1. Limit as [tex]\(x \to \infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex], the quadratic denominator [tex]\(x^2 - 3\)[/tex] grows much faster than the linear numerator [tex]\(x - 6\)[/tex].
- Thus, the value of [tex]\(f(x)\)[/tex] tends to [tex]\(0\)[/tex].

2. Limit as [tex]\(x \to -\infty\)[/tex]:
- Similarly, as [tex]\(x\)[/tex] approaches [tex]\(-\infty\)[/tex], the growing quadratic term in the denominator again causes the fraction to approach [tex]\(0\)[/tex].

This option yields limits of [tex]\(0\)[/tex] in both directions, which does not match the criteria.

### Option C: [tex]\(f(x) = \frac{x + 6}{x - 6}\)[/tex]

1. Limit as [tex]\(x \to \infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex], the leading terms dominate, and the function behaves like [tex]\(\frac{x}{x} = 1\)[/tex].

2. Limit as [tex]\(x \to -\infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(-\infty\)[/tex], the leading terms still dominate and the ratio is the same, so the function behaves like [tex]\(\frac{x}{x} = 1\)[/tex].

This gives us limits of [tex]\(1\)[/tex] in both directions, which also does not align with the criteria.

### Option D: [tex]\(f(x) = \frac{x - 6}{x + 6}\)[/tex]

1. Limit as [tex]\(x \to \infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex], the leading terms dominate, so the function behaves like [tex]\(\frac{x}{x} = 1\)[/tex].

2. Limit as [tex]\(x \to -\infty\)[/tex]:
- As [tex]\(x\)[/tex] approaches [tex]\(-\infty\)[/tex], the function behaves like [tex]\(\frac{-x}{-x} = 1\)[/tex].

This also results in limits of [tex]\(1\)[/tex] in both directions, thus not fulfilling the criteria of going to [tex]\( \infty \)[/tex] and [tex]\(- \infty \)[/tex] respectively.

### Conclusion
Carefully evaluating all options, the function that fits the criteria of approaching [tex]\(\infty\)[/tex] as [tex]\(x \to \infty\)[/tex] and [tex]\(-\infty\)[/tex] as [tex]\(x \to -\infty\)[/tex] is:

None of the above options direct match the criteria stated.

However, assuming there could have been an error, the most plausible answer could be option C: [tex]\(f(x) = \frac{x + 6}{x - 6}\)[/tex] which closely matches the potential criteria if reviewed symbolically and slightly different function constraints or redefinition occur.

Therefore the correct answer based on limits could be assumed is matching thematic solution as option

[tex]\[ \boxed{3} \][/tex]