Let [tex]$f(x)=\frac{x^4-32 x^2}{9}$[/tex].

Sketch the function using a graphing tool and answer the following questions.

(a) Use the definition of a derivative or the derivative rules to find
[tex]\[ f^{\prime}(x)= \ \square \][/tex]

(b) Use the definition of a derivative or the derivative rules to find
[tex]\[ f^{\prime \prime}(x)= \ \square \][/tex]

(c) On what interval is [tex]$f$[/tex] increasing (include the endpoints in the interval)?
[tex]\[ \text{Interval of increasing} = \ \square \][/tex]

(d) On what interval is [tex]$f$[/tex] decreasing (include the endpoints in the interval)?
[tex]\[ \text{Interval of decreasing} = \ \square \][/tex]

(e) On what interval is [tex]$f$[/tex] concave downward (include the endpoints in the interval)?
[tex]\[ \text{Interval of concave downward} = \ \square \][/tex]

(f) On what interval is [tex]$f$[/tex] concave upward (include the endpoints in the interval)?
[tex]\[ \text{Interval of concave upward} = \ \square \][/tex]

Question Help: [tex]\[ \square \][/tex] Video



Answer :

Let's solve the given problem step-by-step:

Consider the function [tex]\( f(x) = \frac{x^4 - 32 x^2}{9} \)[/tex].

### (a) First Derivative [tex]\( f'(x) \)[/tex]

To find the first derivative of [tex]\( f(x) \)[/tex], we will use the rules of differentiation.

[tex]\[ f'(x) = \frac{d}{dx}\left( \frac{x^4 - 32x^2}{9} \right) \][/tex]

Applying the power rule, we get:

[tex]\[ f'(x) = \frac{1}{9} \left( 4x^3 - 64x \right) = \frac{4x^3 - 64x}{9} \][/tex]

So, the first derivative is:

[tex]\[ f'(x) = \frac{4x^3 - 64x}{9} \][/tex]

### (b) Second Derivative [tex]\( f''(x) \)[/tex]

Next, we need to find the second derivative of [tex]\( f(x) \)[/tex].

[tex]\[ f''(x) = \frac{d}{dx}\left( \frac{4x^3 - 64x}{9} \right) \][/tex]

Applying the power rule again, we get:

[tex]\[ f''(x) = \frac{1}{9} \left( 12x^2 - 64 \right) = \frac{12x^2 - 64}{9} = \frac{4x^2 - 64}{3} \][/tex]

So, the second derivative is:

[tex]\[ f''(x) = \frac{4x^2 - 64}{3} \][/tex]

### (c) Interval of Increasing

For the function to be increasing, the first derivative [tex]\( f'(x) \)[/tex] must be greater than 0. We solve for [tex]\( f'(x) > 0 \)[/tex]:

However, the solution reveals that there are no intervals where [tex]\( f'(x) > 0 \)[/tex]. Thus, the function does not have any intervals of increasing.

So, the interval of increasing is:

[tex]\[ \text{interval of increasing} = \emptyset \][/tex]

### (d) Interval of Decreasing

For the function to be decreasing, the first derivative [tex]\( f'(x) \)[/tex] must be less than 0. We solve for [tex]\( f'(x) < 0 \)[/tex]:

Similarly, there are no intervals where [tex]\( f'(x) < 0 \)[/tex]. Thus, the function does not have any intervals of decreasing.

So, the interval of decreasing is:

[tex]\[ \text{interval of decreasing} = \emptyset \][/tex]

### (e) Interval of Concave Downward

For the function to be concave downward, the second derivative [tex]\( f''(x) \)[/tex] must be less than 0. We solve for [tex]\( f''(x) < 0 \)[/tex]:

The solution shows that there are no intervals where [tex]\( f''(x) < 0 \)[/tex]. Thus, the function does not have any intervals of concave downward.

So, the interval of concave downward is:

[tex]\[ \text{interval of concave downward} = \emptyset \][/tex]

### (f) Interval of Concave Upward

For the function to be concave upward, the second derivative [tex]\( f''(x) \)[/tex] must be greater than 0. We solve for [tex]\( f''(x) > 0 \)[/tex]:

The solution shows that there are no intervals where [tex]\( f''(x) > 0 \)[/tex]. Thus, the function does not have any intervals of concave upward.

So, the interval of concave upward is:

[tex]\[ \text{interval of concave upward} = \emptyset \][/tex]

Thus, after careful consideration, we conclude the following intervals:

(a) [tex]\( f'(x) = \frac{4x^3 - 64x}{9} \)[/tex]
(b) [tex]\( f''(x) = \frac{4x^2 - 64}{3} \)[/tex]
(c) Interval of increasing: [tex]\( \emptyset \)[/tex]
(d) Interval of decreasing: [tex]\( \emptyset \)[/tex]
(e) Interval of concave downward: [tex]\( \emptyset \)[/tex]
(f) Interval of concave upward: [tex]\( \emptyset \)[/tex]