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Select the correct answer.

Which function displays this end behavior?

- As \( x \) approaches negative infinity, \( y \) approaches positive infinity.
- As \( x \) approaches positive infinity, \( y \) approaches negative infinity.

A. \( y = -3x^2 + 4 \)
B. \( y = 3(x-1)^2 \)
C. \( y = (x+2)^3 - 9 \)
D. [tex]\( y = -2x^3 \)[/tex]


Sagot :

To determine the function that matches the given end behavior, let's analyze each option step-by-step:

1. Option A: \( y = -3x^2 + 4 \)
- For large negative values of \( x \) (i.e., \( x \to -\infty \)):
[tex]\[ y = -3(-\infty)^2 + 4 \approx -\infty \][/tex]
Thus, as \( x \) approaches negative infinity, \( y \) approaches negative infinity.
- For large positive values of \( x \) (i.e., \( x \to +\infty \)):
[tex]\[ y = -3(\infty)^2 + 4 \approx -\infty \][/tex]
Hence, as \( x \) approaches positive infinity, \( y \) also approaches negative infinity.

2. Option B: \( y = 3(x-1)^2 \)
- For large negative values of \( x \) (i.e., \( x \to -\infty \)):
[tex]\[ y = 3(-\infty - 1)^2 \approx +\infty \][/tex]
So, as \( x \) approaches negative infinity, \( y \) approaches positive infinity.
- For large positive values of \( x \) (i.e., \( x \to +\infty \)):
[tex]\[ y = 3(\infty - 1)^2 \approx +\infty \][/tex]
Therefore, as \( x \) approaches positive infinity, \( y \) also approaches positive infinity.

3. Option C: \( y = (x+2)^3 - 9 \)
- For large negative values of \( x \) (i.e., \( x \to -\infty \)):
[tex]\[ y = (-\infty + 2)^3 - 9 \approx -\infty \][/tex]
Hence, as \( x \) approaches negative infinity, \( y \) also approaches negative infinity.
- For large positive values of \( x \) (i.e., \( x \to +\infty \)):
[tex]\[ y = (\infty + 2)^3 - 9 \approx +\infty \][/tex]
So, as \( x \) approaches positive infinity, \( y \) approaches positive infinity.

4. Option D: \( y = -2x^3 - 1 \)
- For large negative values of \( x \) (i.e., \( x \to -\infty \)):
[tex]\[ y = -2(-\infty)^3 - 1 \approx +\infty \][/tex]
Hence, as \( x \) approaches negative infinity, \( y \) approaches positive infinity.
- For large positive values of \( x \) (i.e., \( x \to +\infty \)):
[tex]\[ y = -2(\infty)^3 - 1 \approx -\infty \][/tex]
Therefore, as \( x \) approaches positive infinity, \( y \) approaches negative infinity.

Based on our analysis, the function that exhibits the correct end behavior (i.e., as \( x \) approaches negative infinity, \( y \) approaches positive infinity, and as \( x \) approaches positive infinity, \( y \) approaches negative infinity) is:

[tex]\[ \boxed{y = -2x^3 - 1} \][/tex]

So the correct answer is D.