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Determine whether Rolle's Theorem can be applied to [tex]\( f \)[/tex] on the closed interval [tex]\([a, b]\)[/tex]. Select all that apply.

[tex]\[ f(x) = x^{2/3} - 8, \quad [-27, 27] \][/tex]

A. Yes, Rolle's Theorem can be applied.
B. No, because [tex]\( f \)[/tex] is not continuous on the closed interval [tex]\([a, b]\)[/tex].
C. No, because [tex]\( f \)[/tex] is not differentiable in the open interval [tex]\((a, b)\)[/tex].
D. No, because [tex]\( f(a) \neq f(b) \)[/tex].

If Rolle's Theorem can be applied, find all values of [tex]\( c \)[/tex] in the open interval [tex]\((a, b)\)[/tex] such that [tex]\( f'(c) = 0 \)[/tex]. Enter a comma-separated list. If Rolle's Theorem cannot be applied, enter NA.

[tex]\[ c = \][/tex]

[tex]\[ \square \][/tex]


Sagot :

To determine whether Rolle's Theorem can be applied to the function [tex]\( f \)[/tex] on the closed interval [tex]\([a, b]\)[/tex], we need to verify the following three conditions of Rolle's Theorem:

1. [tex]\( f \)[/tex] is continuous on the closed interval [tex]\([a, b]\)[/tex].
2. [tex]\( f \)[/tex] is differentiable on the open interval [tex]\((a, b)\)[/tex].
3. [tex]\( f(a) = f(b) \)[/tex].

Let's analyze each condition in detail for the function [tex]\( f(x) = x^{2/3} - 8 \)[/tex] on the interval [tex]\([-27, 27]\)[/tex].

### 1. Continuity

The function [tex]\( f(x) = x^{2/3} - 8 \)[/tex] is a composition of elementary functions [tex]\( x^{2/3} \)[/tex] and a constant [tex]\( -8 \)[/tex]. The function [tex]\( x^{2/3} \)[/tex] is continuous everywhere. Consequently, the function [tex]\( f(x) \)[/tex] is continuous on the closed interval [tex]\([−27, 27]\)[/tex].

### 2. Differentiability

To determine if [tex]\( f \)[/tex] is differentiable on the open interval [tex]\((a, b) = (−27, 27)\)[/tex], we take the derivative of [tex]\( f \)[/tex]:

[tex]\[ f'(x) = \frac{d}{dx}(x^{2/3} - 8) \][/tex]
[tex]\[ f'(x) = \frac{2}{3}x^{-1/3} \][/tex]

The function [tex]\( f'(x) = \frac{2}{3}x^{-1/3} \)[/tex] is not defined at [tex]\(x = 0\)[/tex] because it involves a negative fractional power of [tex]\( x \)[/tex]. This means [tex]\( f \)[/tex] is not differentiable at [tex]\( x = 0 \)[/tex]. Therefore, [tex]\( f \)[/tex] is not differentiable on the entire open interval [tex]\((−27, 27)\)[/tex].

### 3. Equal Function Values at Endpoints

Next, we check if [tex]\( f(a) = f(b) \)[/tex]:
[tex]\[ f(-27) = (-27)^{2/3} - 8 = 9 - 8 = 1 \][/tex]
[tex]\[ f(27) = 27^{2/3} - 8 = 9 - 8 = 1 \][/tex]

Since [tex]\( f(-27) = f(27) \)[/tex], this condition is satisfied.

### Conclusion

Rolle's Theorem cannot be applied because the function [tex]\( f(x) \)[/tex] is not differentiable at [tex]\( x = 0 \)[/tex] within the open interval [tex]\( (-27, 27) \)[/tex].

### Values of [tex]\( c \)[/tex]

Since Rolle's Theorem cannot be applied, we should enter "NA" for the values of [tex]\( c \)[/tex]:

[tex]\[ c = \boxed{\text{NA}} \][/tex]

So summarizing the answers, the appropriate response is:
- No, because [tex]\( f \)[/tex] is not differentiable in the open interval [tex]\( (a, b) \)[/tex].

And for the values of [tex]\( c \)[/tex]:
[tex]\[ c = \boxed{\text{NA}} \][/tex]
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