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Ch. 4 - Applications of the Derivative
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 4, Problem 4.8.58b

{Use of Tech} Fixed points of quadratics and quartics Let f(x) = ax(1 -x), where a is a real number and 0 ≤ a ≤ 1. Recall that the fixed point of a function is a value of x such that f(x) = x (Exercises 48–51). 


b. Consider the polynomial g(x) = f(f(x)). Write g in terms of a and powers of x. What is its degree?

Verified step by step guidance
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First, understand that a fixed point of a function f(x) is a value x such that f(x) = x. For the function f(x) = ax(1 - x), we need to find f(f(x)) to form the polynomial g(x).
Start by substituting f(x) into itself: f(f(x)) = a(f(x))(1 - f(x)). This means we need to substitute f(x) = ax(1 - x) into the expression again.
Calculate f(x) = ax(1 - x) and substitute it into the expression: f(f(x)) = a(ax(1 - x))(1 - ax(1 - x)).
Simplify the expression: Expand the terms inside the parentheses and multiply them out. This will involve expanding (1 - ax(1 - x)) and multiplying it by ax(1 - x).
Determine the degree of the polynomial g(x): After simplifying, observe the highest power of x in the expression. The degree of g(x) will be the highest power of x present in the expanded form.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fixed Points

A fixed point of a function is a value of x for which the function evaluates to the same value, meaning f(x) = x. This concept is crucial in understanding the behavior of functions, particularly in iterative processes and stability analysis. In the context of the given function f(x) = ax(1 - x), finding fixed points involves solving the equation ax(1 - x) = x.
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Critical Points

Composition of Functions

The composition of functions involves applying one function to the result of another. In this case, g(x) = f(f(x)) means we first apply f to x, and then apply f again to the result. Understanding function composition is essential for manipulating and simplifying expressions, especially when dealing with polynomials and their degrees.
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Degree of a Polynomial

The degree of a polynomial is the highest power of the variable in the polynomial expression. It provides insight into the polynomial's behavior, such as the number of roots and the end behavior of the graph. For the polynomial g(x) derived from f(f(x)), determining its degree involves analyzing the composition and identifying the maximum exponent of x in the resulting expression.
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Related Practice
Textbook Question

107–110. {Use of Tech} Motion with gravity Consider the following descriptions of the vertical motion of an object subject only to the acceleration due to gravity. Begin with the acceleration equation a(t) = v' (t) = -g , where g = 9.8 m/s² .

b. Find the position of the object for all relevant times. 

A payload is released at an elevation of 400 m from a hot-air balloon that is rising at a rate of 10 m/s.

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Textbook Question

Suppose S = x + 2y is an objective function subject to the constraint xy = 50, for x > 0 and y > 0.

b. Find the absolute minimum value of S subject to the given constraint.

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Textbook Question

{Use of Tech} Basketball shot A basketball is shot with an initial velocity of v ft/s at an angle of 45° to the floor. The center of the basketball is 8 ft above the floor at a horizontal distance of 18 feet from the center of the basketball hoop when it is released. The height h (in feet) of the center of the basketball after it has traveled a horizontal distance of x feet is modeled by the function h(x) = 32x² / v² + x + 8 (see figure). <IMAGE>



b. During the flight of the basketball, show that the distance s from the center of the basketball to the front of the hoop is s = √ (x - 17.25)² + ( -(4x² / 81) + x - 2)² (Hint: The diameter of the basketball hoop is 18 inches.) 

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Textbook Question

{Use of Tech} A damped oscillator The displacement of an object as it bounces vertically up and down on a spring is given by y(t) = 2.5e⁻ᵗ cos 2t, where the initial displacement is y(0) = 2.5 and y = 0 corresponds to the rest position (see figure). <IMAGE>

b. Find the time and the displacement when the object reaches its lowest point.

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Textbook Question

Cylinder in a cone A right circular cylinder is placed inside a cone of radius R and height H so that the base of the cylinder lies on the base of the cone.


b. Find the dimensions of the cylinder with maximum lateral surface area (area of the curved surface).

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Textbook Question

{Use of Tech} Every second counts You must get from a point P on the straight shore of a lake to a stranded swimmer who is 50 from a point Q on the shore that is 50 m from you (see figure). Assuming that you can swim at a speed of 2 m/s and run at a speed of 4 m/s, the goal of this exercise is to determine the point along the shore, x meters from Q, where you should stop running and start swimming to reach the swimmer in the minimum time. <IMAGE>


b. Find the critical point of T on (0, 50).

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