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Using a calculator or computer, graph the functions in Problems \(8-13 .\) Describe in words the interesting features of the graph, including the location of the critical points and where the function is monotonic (that is, increasing or decreasing). Then use the derivative and algebra to explain the shape of the graph. $$f(x)=x^{3}+6 x+1$$

Short Answer

Expert verified
The function is monotonically increasing with no real critical points.

Step by step solution

01

Graph the Function

Use a graphing calculator or computer software to plot the function \( f(x) = x^3 + 6x + 1 \). Observe the overall shape and important features of the graph, such as peaks, valleys, and where the function increases or decreases.
02

Identify Critical Points

To find the critical points, first calculate the derivative of the function. The derivative \( f'(x) \) of the function \( f(x) = x^3 + 6x + 1 \) is \( f'(x) = 3x^2 + 6 \). Set the derivative equal to zero to find the critical points: \( 3x^2 + 6 = 0 \).
03

Solve for Critical Points

Solve the equation \( 3x^2 + 6 = 0 \) for \( x \):\[3x^2 = -6 \] \[ x^2 = -2 \]. Since the equation \( x^2 = -2 \) does not have real solutions, there are no real critical points for this function.
04

Determine Monotonicity Intervals

Since the critical points do not exist in the real number system, the sign of the derivative \( f'(x) = 3x^2 + 6 \) is always positive for all real numbers. Therefore, the function is monotonically increasing on the entire real line.
05

Analyze the Graph's Shape Using the Derivative

The fact that \( f'(x) = 3x^2 + 6 \) is always positive indicates that the function is continuously increasing without any local maxima or minima. This aligns with the observed shape of the graph and shows no turning points exist.

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Key Concepts

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

Critical points
Critical points are vital in understanding the behavior of a graph. These are the points where the function's derivative is zero or does not exist. They indicate potential places where the function might change direction, such as peaks or valleys. To find the critical points for the function \( f(x) = x^3 + 6x + 1 \), we must first compute its derivative. For our function, the derivative is \( f'(x) = 3x^2 + 6 \). Setting this equal to zero gives the equation \( 3x^2 + 6 = 0 \). Solving \( 3x^2 = -6 \), leads us to \( x^2 = -2 \), which does not have real solutions. This indicates there are no real critical points. Understanding this concept helps comprehend that not all functions have critical points in the realm of real numbers, and thus may not have local minimums or maximums.
Monotonicity
Monotonicity describes how a function behaves as it moves along the x-axis. A function is either increasing, decreasing, or constant over specific intervals. To determine the monotonicity of \( f(x) = x^3 + 6x + 1 \), we'll use the derivative we found earlier: \( f'(x) = 3x^2 + 6 \).Since there are no real critical points and the expression \( 3x^2 + 6 \) is always greater than zero for all real numbers, it tells us that the function is monotonically increasing across its entire domain. This means, as you move from left to right on the graph, the function's output values also consistently increase, with no declines.Recognizing this property is crucial for visual analysis. It indicates that the graph won’t have any peaks or valleys; rather, it moves upwards consistently.
Derivative analysis
Derivative analysis is a key tool for explaining a function's graph shape. It involves understanding how the derivative affects the function's behavior. For \( f(x) = x^3 + 6x + 1 \), the derivative \( f'(x) = 3x^2 + 6 \) offers valuable insights.Because \( f'(x) \) is always positive (due to \( 3x^2 \) being non-negative and 6 being positive), we conclude the function is not only increasing but does so without interruptions. The graph will slope upwards consistently, matching what is observed visually. This analysis confirms the absence of local extrema—places where the function changes from increasing to decreasing or vice versa.Utilizing derivative analysis provides a deeper understanding of why a graph appears the way it does. It's an essential method for comprehending the underlying terms of equations and their visual representations.

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