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25-40 Find the critical numbers of the function. $$f(x)=x^{3}+3 x^{2}-24 x$$

Short Answer

Expert verified
The critical numbers are \( x = 2 \) and \( x = -4 \).

Step by step solution

01

Find the derivative

To find the critical numbers of the function, first, we need to find its derivative. Given the function \[ f(x) = x^3 + 3x^2 - 24x \]Take the derivative with respect to \( x \):\[ f'(x) = 3x^2 + 6x - 24 \]
02

Set the derivative to zero

To find the critical points, set the derivative equal to zero and solve for \( x \):\[ 3x^2 + 6x - 24 = 0 \]
03

Simplify the equation

Simplify the quadratic equation by dividing everything by 3 to make calculations easier:\[ x^2 + 2x - 8 = 0 \]
04

Solve the quadratic equation

Solve the quadratic equation \( x^2 + 2x - 8 = 0 \) using the quadratic formula:\[ x = \frac{{-b \pm \sqrt{{b^2 - 4ac}}}}{2a} \]Here, \( a = 1 \), \( b = 2 \), and \( c = -8 \). Substitute these values into the formula:\[ x = \frac{{-2 \pm \sqrt{{2^2 - 4 \cdot 1 \cdot (-8)}}}}{2} = \frac{{-2 \pm \sqrt{{4 + 32}}}}{2} = \frac{{-2 \pm \sqrt{36}}}{2} \]\[ x = \frac{{-2 \pm 6}}{2} \]This gives us two solutions:\[ x = \frac{4}{2} = 2 \]\[ x = \frac{-8}{2} = -4 \]
05

State the critical numbers

The critical numbers are the values of \( x \) where the derivative equals zero. From our calculations, the critical numbers are:\[ x = 2 \text{ and } x = -4 \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Derivative
In mathematics, the derivative of a function represents the rate at which the function's value changes as its input changes. It's like determining the slope or steepness of the function at any point on its curve. To find the derivative, we apply rules of differentiation which involve taking the function and systematically computing its change. In the case of the given function, \[ f(x) = x^3 + 3x^2 - 24x \]we applied differentiation rules to acquire:\[ f'(x) = 3x^2 + 6x - 24 \]This derivative function now tells us how the original function \( f(x) \) behaves or changes at each value of \( x \). When we talk about finding critical numbers, we look for where this derivative equals zero because those are points where the rate of change "slows" to zero, often indicating maxima, minima, or points of inflection.
Quadratic Equation
A quadratic equation is a type of polynomial that involves terms up to the second degree, written in the general form:\[ ax^2 + bx + c = 0 \]In our exercise, after finding the derivative, we simplified it:\[ 3x^2 + 6x - 24 = 0 \]This was then divided by 3 to ease calculations:\[ x^2 + 2x - 8 = 0 \]This simplifies the problem and helps find values where the derivative is zero. Those solutions give us the desired critical points. Quadratic equations are pivotal in many areas of math as they frequently occur in various types of function analysis, including those examining physical phenomena like projectile motion.
Quadratic Formula
The quadratic formula is a tool used to find the solutions of a quadratic equation. It works for any quadratic equation of the form:\[ ax^2 + bx + c = 0 \]The formula itself is:\[ x = \frac{{-b \pm \sqrt{{b^2 - 4ac}}}}{2a} \]In our solution, to find the critical numbers, we used this formula on the simplified equation:\[ x^2 + 2x - 8 = 0 \]For this equation, by setting \( a = 1 \), \( b = 2 \), and \( c = -8 \), we calculated:\[ x = \frac{{-2 \pm \sqrt{36}}}{2} \]This resulted in \( x = 2 \) and \( x = -4 \). These are the critical numbers where the first derivative is zero, indicating points of interest in the behavior of the original function.
Function Analysis
Function analysis involves studying the properties and behavior of functions, aiming to understand how changes in \( x \) affect the function's output. It involves investigating maxima, minima, and intervals of increase or decrease. When we look at the critical numbers found (\( x = 2 \) and \( x = -4 \)), these numbers tell us where the function's slope changes direction. - **Critical Points:** These are where the derivative is zero.- **Local Maximum and Minimum:** Analysis involves checking whether these points are peaks or troughs.To do this, we often use techniques such as:- **First Derivative Test:** Determines if the function changes from increasing to decreasing.- **Second Derivative Test:** Confirms the concavity and nature (maxima or minima).Analyzing functions allows us to predict and model real-world phenomena effectively, explaining why this type of mathematics is so powerful and essential in application.

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