Chapter 10: Problem 24
a. For \(f(x)=3 x^{2}-4 x+5,\) find the second Taylor polynomial at \(x=2\) b. Multiply out the Taylor polynomial found in part (a) and show that it is equal to the original polynomial.
Short Answer
Expert verified
The second Taylor polynomial is \( 3x^2 - 4x + 5 \), matching the original polynomial.
Step by step solution
01
Identify Function and Derivatives
The given function is \( f(x) = 3x^2 - 4x + 5 \). We need the first and second derivatives of the function at \( x = 2 \). Let's compute them:- \( f'(x) = 6x - 4 \)- \( f''(x) = 6 \).Now evaluate these derivatives at \( x = 2 \):- \( f(2) = 3(2)^2 - 4(2) + 5 = 12 - 8 + 5 = 9 \)- \( f'(2) = 6(2) - 4 = 12 - 4 = 8 \)- \( f''(2) = 6 \).
02
Write the Taylor Polynomial Formula
The general formula for the second Taylor polynomial \( P_2(x) \) of \( f(x) \) centered at \( a \) is:\[ P_2(x) = f(a) + f'(a)(x - a) + \frac{f''(a)}{2!}(x - a)^2 \]In this problem, \( a = 2 \).
03
Substitute and Simplify the Taylor Polynomial
Substitute the values from Step 1 into the Taylor polynomial formula:\[ P_2(x) = 9 + 8(x - 2) + \frac{6}{2}(x - 2)^2 \]Simplify:\[ P_2(x) = 9 + 8(x - 2) + 3(x - 2)^2 \].
04
Expand the Taylor Polynomial
Now, expand the polynomial \( P_2(x) \):Start with \( (x-2)^2 = x^2 - 4x + 4 \).Insert into the polynomial:\[ P_2(x) = 9 + 8(x - 2) + 3(x^2 - 4x + 4) \]Expand each term:\[ = 9 + 8x - 16 + 3x^2 - 12x + 12 \]Combine like terms:\[ P_2(x) = 3x^2 - 4x + 5 \].
05
Verify Equality to Original Polynomial
The expanded Taylor polynomial \( 3x^2 - 4x + 5 \) matches the original polynomial \( f(x) = 3x^2 - 4x + 5 \), confirming that they are indeed equal.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
Derivatives are a fundamental concept in calculus. A derivative represents the rate at which a function is changing at any given point. For a function like our polynomial, the derivative can tell us how steep the curve is at different points.
- The first derivative, denoted as \(f'(x)\), provides the slope of the tangent line to the curve at any point \(x\).
- The second derivative, \(f''(x)\), gives us information about the curvature or concavity of the function.
Polynomial Expansion
Polynomial expansion involves multiplying out expressions to convert them into a standard polynomial form. This step is crucial for simplifying the Taylor polynomial into a form that is easy to compare with the original function. In the process, we took:\[ P_2(x) = 9 + 8(x - 2) + 3(x^2 - 4x + 4) \]and expanded it step-by-step. By distributing and combining like terms, we converted each component into a single polynomial:\[ = 9 + 8x - 16 + 3x^2 - 12x + 12 \]This gives us:\[ 3x^2 - 4x + 5 \]Notice how each term fits perfectly, helping to verify that our Taylor-polynomial approach matches the original function.
Function Analysis
Function analysis involves examining the behavior and properties of a function. In this context, it means considering the original polynomial function \(f(x) = 3x^2 - 4x + 5\), its derivatives, and how these relate to the Taylor polynomial.
- The function is a quadratic polynomial, implying it's a parabolic curve opening upwards since the coefficient of \(x^2\) is positive.
- The analysis includes the slope and concavity derived from the derivatives: \(f'(x)\) and \(f''(x)\).
Second Taylor Polynomial
The second Taylor polynomial provides an approximation of a function around a specific point, offering insights into the function's behavior. It is particularly useful for predicting values near this point without evaluating the entire function.In our exercise, the formula used for a second Taylor polynomial centered around \(x = 2\) was:\[ P_2(x) = f(2) + f'(2)(x - 2) + \frac{f''(2)}{2}(x - 2)^2 \]By plugging in values derived from earlier component calculations:\[ P_2(x) = 9 + 8(x - 2) + 3(x - 2)^2 \]We see this polynomial replicates the behavior of the original function around the point \(x = 2\). The expansion and simplification confirm that it returns to the original function after full manipulation, showcasing the power and accuracy of using Taylor polynomials for function approximation.