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Determine all critical points for the function [tex]\( f(x) = x^3 - 12x + 5 \)[/tex].

To find the critical points, we need to solve for [tex]\( f'(x) = 0 \)[/tex].

1. [tex]\( f'(x) = 3x^2 - 12 \)[/tex]
2. Set [tex]\( 3x^2 - 12 = 0 \)[/tex]
3. Solving, we get:
[tex]\[ \sqrt{x^2} = \sqrt{4} \][/tex]
[tex]\[ x = \pm 2 \][/tex]

The critical points are [tex]\( x = 2 \)[/tex] and [tex]\( x = -2 \)[/tex].

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The position of a body moving on a coordinate line is given by [tex]\( s = t^2 - 7t + 6 \)[/tex], with [tex]\( s \)[/tex] in meters and [tex]\( t \)[/tex] in seconds. When, if ever, during the interval [tex]\( 0 \leq t \leq 7 \)[/tex] does the body change direction?

To determine when the body changes direction, we need to find when [tex]\( v(t) = s'(t) = 0 \)[/tex]:

1. [tex]\( s'(t) = 2t - 7 \)[/tex]
2. Set [tex]\( 2t - 7 = 0 \)[/tex]
3. Solving, we get:
[tex]\[ t = 3.5 \][/tex]

The body changes direction at [tex]\( t = 3.5 \)[/tex] seconds within the interval [tex]\( 0 \leq t \leq 7 \)[/tex].

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Find the derivative of [tex]\( y = \left( \frac{1}{x^2} + 2 \right) \left( x^2 - \frac{1}{x^2} + 2 \right) \)[/tex].

A) [tex]\( -\frac{4}{x^5} - 4x \)[/tex]
B) [tex]\( \frac{4}{x^3} + 4x \)[/tex]
C) [tex]\( \frac{4}{x^5} + 4x \)[/tex]
D) [tex]\( -\frac{1}{x^5} \)[/tex]


Sagot :

Let's address each part of your question in a detailed, step-by-step manner.

### 4) Finding the critical points for [tex]\( f(x) = x^3 - 12x + 5 \)[/tex]

To find the critical points of the function, we need to identify where the first derivative equals zero or does not exist.

1. Compute the first derivative of [tex]\( f(x) \)[/tex]:
[tex]\[ f'(x) = \frac{d}{dx}(x^3 - 12x + 5) = 3x^2 - 12. \][/tex]

2. Set the first derivative equal to zero and solve for [tex]\( x \)[/tex]:
[tex]\[ 3x^2 - 12 = 0. \][/tex]

3. Solve the equation:
[tex]\[ 3x^2 = 12 \implies x^2 = 4 \implies x = \pm 2. \][/tex]

Thus, the critical points are at [tex]\( x = 2 \)[/tex] and [tex]\( x = -2 \)[/tex].

### 5) Change of direction for the position function [tex]\( s(t) = t^2 - 7t + 6 \)[/tex] within [tex]\( 0 \leq t \leq 7 \)[/tex]

To determine when the body changes direction, we need to find when the velocity [tex]\( \frac{ds}{dt} \)[/tex] changes sign. This happens when [tex]\( \frac{ds}{dt} = 0 \)[/tex].

1. Compute the first derivative of [tex]\( s(t) \)[/tex]:
[tex]\[ \frac{ds}{dt} = \frac{d}{dt}(t^2 - 7t + 6) = 2t - 7. \][/tex]

2. Set the first derivative equal to zero and solve for [tex]\( t \)[/tex]:
[tex]\[ 2t - 7 = 0 \implies t = \frac{7}{2} = 3.5. \][/tex]

3. Check if [tex]\( t = 3.5 \)[/tex] is within the interval [tex]\( 0 \leq t \leq 7 \)[/tex]:
Indeed, [tex]\( 3.5 \)[/tex] is in the interval.

Hence, the body changes direction at [tex]\( t = 3.5 \)[/tex] seconds.

### 6) Derivative of [tex]\( y = \left(\frac{1}{x^2} + 2\right)\left(x^2 - \frac{1}{x^2} + 2\right) \)[/tex]

To find the derivative, we use the product rule [tex]\( (uv)' = u'v + uv' \)[/tex].

1. Let [tex]\( u = \frac{1}{x^2} + 2 \)[/tex] and [tex]\( v = x^2 - \frac{1}{x^2} + 2 \)[/tex].

2. First, compute the derivatives of [tex]\( u \)[/tex] and [tex]\( v \)[/tex]:
[tex]\[ u = \frac{1}{x^2} + 2 \implies u' = -\frac{2}{x^3}, \][/tex]
[tex]\[ v = x^2 - \frac{1}{x^2} + 2 \implies v' = 2x + \frac{2}{x^3}. \][/tex]

3. Apply the product rule:
[tex]\[ y' = u'v + uv' = \left(-\frac{2}{x^3}\right)\left(x^2 - \frac{1}{x^2} + 2\right) + \left(\frac{1}{x^2} + 2\right)\left(2x + \frac{2}{x^3}\right). \][/tex]

Simplify each term separately:
[tex]\[ u'v = \left(-\frac{2}{x^3}\right)\left(x^2 - \frac{1}{x^2} + 2\right) = -\frac{2x^2}{x^3} + \frac{2}{x^5} - \frac{4}{x^3} = -\frac{2}{x} + \frac{2}{x^5} - \frac{4}{x^3}, \][/tex]
[tex]\[ uv' = \left(\frac{1}{x^2} + 2\right)\left(2x + \frac{2}{x^3}\right) = \frac{2x}{x^2} + 4x + \frac{2}{x^5} + \frac{4}{x^3} = \frac{2}{x} + 4x + \frac{2}{x^5} + \frac{4}{x^3}. \][/tex]

Combine both results:
[tex]\[ y' = \left(-\frac{2}{x} + \frac{2}{x^5} - \frac{4}{x^3}\right) + \left(\frac{2}{x} + 4x + \frac{2}{x^5} + \frac{4}{x^3}\right) = 4x + \frac{4}{x^5}. \][/tex]

Thus, the correct derivative is:
[tex]\[ y' = 4x + \frac{4}{x^5}. \][/tex]

So, the correct answer is:
[tex]\[ \boxed{C) \frac{4}{x^5} + 4x} \][/tex]