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Express \(p(x)=x^{3}\) as a Taylor polynomial about \(a=\frac{1}{2}\)

Short Answer

Expert verified
The Taylor polynomial for \(x^3\) about \(a=\frac{1}{2}\) is \(T_3(x) = \frac{1}{8} + \frac{3}{4}(x-\frac{1}{2}) + \frac{3}{2}(x^2-x+\frac{1}{4}) + (x^3-\frac{3}{2}x^2+\frac{3}{4}x-\frac{1}{8})\).

Step by step solution

01

Understand the Taylor Polynomial

A Taylor polynomial for a function centered at a point \(a\) approximates the function using its derivatives at \(a\). For a function \(p(x)\), the Taylor polynomial of degree \(n\) about \(a\) is given by:\[ T_n(x) = p(a) + p'(a)(x-a) + \frac{p''(a)}{2!}(x-a)^2 + \frac{p'''(a)}{3!}(x-a)^3 + \ldots + \frac{p^{(n)}(a)}{n!}(x-a)^n \]
02

Find Derivatives of the Function

The function given is \(p(x) = x^3\). Compute its derivatives at least up to the third derivative:- Zero derivative (original function): \(p(x) = x^3\)- First derivative: \(p'(x) = 3x^2\)- Second derivative: \(p''(x) = 6x\)- Third derivative: \(p'''(x) = 6\)
03

Evaluate Derivatives at the Point \(a = \frac{1}{2}\)

Now calculate the value of the function and its derivatives at \(a = \frac{1}{2}\):- \(p(\frac{1}{2}) = (\frac{1}{2})^3 = \frac{1}{8}\)- \(p'(\frac{1}{2}) = 3(\frac{1}{2})^2 = \frac{3}{4}\)- \(p''(\frac{1}{2}) = 6(\frac{1}{2}) = 3\)- \(p'''(\frac{1}{2}) = 6\)
04

Construct the Taylor Polynomial

Substitute these values into the Taylor polynomial formula for \(n = 3\):\[ T_3(x) = \frac{1}{8} + \frac{3}{4}(x-\frac{1}{2}) + \frac{3}{2!}(x-\frac{1}{2})^2 + \frac{6}{3!}(x-\frac{1}{2})^3 \]Calculate each term:- Linear term: \(\frac{3}{4}(x-\frac{1}{2})\)- Quadratic term: \(\frac{3}{2}(x-\frac{1}{2})^2 = \frac{3}{2}(x^2 - x + \frac{1}{4})\)- Cubic term: \(\frac{6}{6}(x-\frac{1}{2})^3 = (x^3 - \frac{3}{2}x^2 + \frac{3}{4}x - \frac{1}{8})\)
05

Simplify the Taylor Polynomial

Combine all the terms to get the simplified Taylor polynomial:\[ T_3(x) = \frac{1}{8} + \frac{3}{4}(x-\frac{1}{2}) + \frac{3}{2}(x^2 - x + \frac{1}{4}) + (x^3 - \frac{3}{2}x^2 + \frac{3}{4}x - \frac{1}{8}) \]Simplify the expression to obtain the final polynomial.

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Key Concepts

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

Derivatives
When working with Taylor polynomials, derivatives play a crucial role. They measure how a function changes as its input changes.
The derivative of a function at a particular point gives us the slope of the tangent to the function at that point.
This is important because it allows us to approximate the function near this point.For the function given in the problem, \(p(x) = x^3\), the derivatives are computed as follows:
  • Zero derivative (the function itself): \(p(x) = x^3\)
  • First derivative: \(p'(x) = 3x^2\)
  • Second derivative: \(p''(x) = 6x\)
  • Third derivative: \(p'''(x) = 6\)
The task here is to understand how these derivatives change when we evaluate them at different points, specifically at \(a=\frac{1}{2}\) for this exercise. This is a step towards building the Taylor polynomial.
Polynomial Approximation
Taylor polynomials are a great tool for approximating functions using polynomials.
The approximation is centered around a particular point, and it uses the value of the function and its derivatives at this point.When constructing a Taylor polynomial, you start with the basic formula:\[ T_n(x) = p(a) + p'(a)(x-a) + \frac{p''(a)}{2!}(x-a)^2 + \ldots + \frac{p^{(n)}(a)}{n!}(x-a)^n \]This equation is key to constructing an approximation that closely follows the shape of the original function near the chosen point.In this exercise, our function is \(p(x) = x^3\) and we want to find the Taylor polynomial centered around \(a=\frac{1}{2}\).
The degree of the polynomial, \(n\), determines how well the approximation can potentially fit the original function.
Higher degrees generally mean a better fit when evaluated closer to the center \(a\). However, it also means more complexity. Understanding this balance is essential in using polynomial approximations effectively.
Function Evaluation
The process of function evaluation in the context of Taylor polynomials involves computing the function and its derivatives at the point \(a\).
This is an essential part of constructing the polynomial, as it allows each term to reflect the behavior of the original function at and near \(a\).To evaluate the function for \(p(x) = x^3\) and its derivatives at \(a=\frac{1}{2}\), we do the following calculations:
  • Function value: \(p(\frac{1}{2}) = (\frac{1}{2})^3 = \frac{1}{8}\)
  • First derivative: \(p'(\frac{1}{2}) = 3(\frac{1}{2})^2 = \frac{3}{4}\)
  • Second derivative: \(p''(\frac{1}{2}) = 6(\frac{1}{2}) = 3\)
  • Third derivative: \(p'''(\frac{1}{2}) = 6\)
These evaluations provide the necessary coefficients when substituting back into the Taylor polynomial formula.
This step ensures that the polynomial we construct is in alignment with the behavior and unique features of the function at the point we are interested.

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Most popular questions from this chapter

Define linear transformations \(S: \mathscr{P}_{n} \rightarrow \mathscr{P}_{n}\) and \(T: \mathscr{P}_{n} \rightarrow \mathscr{P}_{n}\) by \\[ S(p(x))=p(x+1) \text { and } T(p(x))=p^{\prime}(x) \\] Find \((S \circ T)(p(x))\) and \((T \circ S)(p(x)) .[\) Hint: Remember the Chain Rule.

$$\text { Show that } \mathscr{C}[0,1] \cong \mathscr{C}[0,2]$$

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A pendulum consists of a mass, called a bob, that is affixed to the end of a string of length \(L\) (see Figure 6.26 ). When the bob is moved from its rest position and released, it swings back and forth. The time it takes the pendulum to swing from its farthest right position to its farthest left position and back to its next farthest right position is called the period of the pendulum. (Figure can't copy) Let \(\theta=\theta(t)\) be the angle of the pendulum from the vertical. It can be shown that if there is no resistance, then when \(\theta\) is small it satisfies the differential equation \\[ \theta^{\prime \prime}+\frac{g}{L} \theta=0 \\] where \(g\) is the constant of acceleration due to gravity, approximately \(9.7 \mathrm{m} / \mathrm{s}^{2}\). Suppose that \(L=1 \mathrm{m}\) and that the pendulum is at rest (i.e., \(\theta=0\) ) at time \(t=0\) second. The bob is then drawn to the right at an angle of \(\theta_{1}\) radians and released. (a) Find the period of the pendulum. (b) Does the period depend on the angle \(\theta_{1}\) at which the pendulum is released? This question was posed and answered by Galileo in \(1638 .\) [Galileo Galilei \((1564-1642)\) studied medicine as a student at the University of Pisa, but his real interest was always mathematics. In \(1592,\) Galileo was appointed professor of mathematics at the University of Padua in Venice, where he taught primarily geometry and astronomy. He was the first to use a telescope to look at the stars and planets, and in so doing, he produced experimental data in support of the Copernican view that the planets revolve around the sun and not the earth. For this, Galileo was summoned before the Inquisition, placed under house arrest, and forbidden to publish his results. While under house arrest, he was able to write up his research on falling objects and pendulums. His notes were smuggled out of Italy and published as Discourses on Two New Sciences in 1638.]

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