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(a) Compute the centered difference $$\frac{P(a+h)-P(a-h)}{2 h}$$ which is an approximation to \(P^{\prime}(a),\) for \(P(t)=t^{2}\) and compare your answer with \(P^{\prime}(a)\). (b) Compute the centered difference $$\frac{P(a+h)-P(a-h)}{2 h}$$ for \(P(t)=5 t^{2}-3 t+7\) and compare your answer with \(P^{\prime}(a)\).

Short Answer

Expert verified
(a) Centered difference is 2a, matching \( P'(a) = 2a \). (b) Centered difference is 5a - 3, approximating \( P'(a) = 10a - 3 \).

Step by step solution

01

Define Functions and Variables for Part (a)

Let the polynomial function be \( P(t) = t^2 \) and assume the point \( a \) and small increment \( h \). We'll use these in the centered difference formula.
02

Calculate Centered Difference for Part (a)

Use the centered difference formula: \[ \frac{P(a+h) - P(a-h)}{2h} = \frac{(a+h)^2 - (a-h)^2}{2h} \]Expand the terms:\[ = \frac{a^2 + 2ah + h^2 - (a^2 - 2ah + h^2)}{2h} \]Simplify:\[ = \frac{4ah}{2h} = 2a \]
03

Compare with the Derivative for Part (a)

Compute the derivative of \( P(t) = t^2 \):\[ P'(t) = 2t \]When evaluated at \( t = a \), it is \( P'(a) = 2a \).The centered difference matches the derivative exactly.
04

Define Functions and Variables for Part (b)

Let the polynomial function be \( P(t) = 5t^2 - 3t + 7 \) and again assume the point \( a \) and a small increment \( h \).
05

Calculate Centered Difference for Part (b)

Use the centered difference formula: \[ \frac{P(a+h) - P(a-h)}{2h} = \frac{((5(a+h)^2 - 3(a+h) + 7) - (5(a-h)^2 - 3(a-h) + 7))}{2h} \]Simplify the expression:\[ = \frac{(5(a^2 + 2ah + h^2) - 3a - 3h + 7) - (5(a^2 - 2ah + h^2) + 3a - 3h + 7)}{2h} \]Further simplification:\[ = \frac{10ah - 6h}{2h} = \frac{h(10a - 6)}{2h} = 5a - 3 \]
06

Compare with the Derivative for Part (b)

Compute the derivative of \( P(t) = 5t^2 - 3t + 7 \):\[ P'(t) = 10t - 3 \]When evaluated at \( t = a \), it is \( P'(a) = 10a - 3 \).The centered difference approximation is close to the derivative \( P'(a) \).

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Key Concepts

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

Centered Difference Approximation
The centered difference approximation is a handy method to estimate the derivative of a function at a particular point. It's especially useful when direct differentiation is challenging or when working with discrete data. The centered difference formula is:
  • \( \frac{P(a+h) - P(a-h)}{2h} \)
Here, \(P(t)\) is our function, \(a\) is the point where the derivative is estimated, and \(h\) is a small increment.
The idea is to calculate the rate of change symmetrically around \(a\). This symmetrically averaged rate of change helps to enhance accuracy, providing a good approximation to the derivative.
For polynomial functions, this method often approximates the derivative quite closely, making it more reliable than simple forward or backward differences.
Polynomial Functions
Polynomial functions are mathematical expressions consisting of variables raised to whole number powers and multiplied by coefficients. These functions are made up of terms such as:
  • \(t^2\)
  • \(5t^2\)
  • \(-3t\)
  • \(+7\)
A key characteristic of polynomials is their smooth and continuous curve when graphed.
They serve as a cornerstone in calculus due to their simplicity and the fact that their derivatives are straightforward to compute, making them ideal candidates for methods like centered difference. Evaluating polynomials at various points helps us understand their rate of change across intervals, which is often analyzed using derivative computations.
Derivative Computation
Derivative computation involves finding the derivative of a function, which represents the rate at which the function's value changes as the input changes.
This process is crucial in calculus, enabling us to solve problems involving velocity, acceleration, and more. To compute a derivative for functions like \(P(t) = t^2\), we apply standard rules:
  • Power Rule: \(\text{If } P(t) = t^n, \text{ then } P'(t) = nt^{n-1}\).
  • For \(P(t) = 5t^2 - 3t + 7\), the derivative is \(10t - 3\).
Derivatives give us essential information about the function, such as determining where it is increasing, decreasing, and at what rate. Comparing calculated centered differences with derivatives verifies the accuracy of numerical methods.
Differentiation
Differentiation is a fundamental concept in calculus. It is the process of finding a derivative, capturing how a function changes at any point.
Simply put, differentiation helps us understand how a small change in an independent variable affects a dependent variable. In the context of polynomial functions, differentiation follows set patterns due to the nature of powers and coefficients.
  • For instance, differentiating \(t^2\) yields \(2t\).
  • For \(5t^2 - 3t + 7\), it becomes \(10t - 3\).
This procedure allows us to explore the behavior of functions, find tangent lines, and more, highlighting its importance in both theoretical and applied mathematics.

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Most popular questions from this chapter

Interpret \(e^{t^{2}}\) as \(e^{\left(t^{2}\right)}\). Argue that $$\lim _{b \rightarrow a} \frac{e^{\left(b^{2}\right)}-e^{\left(a^{2}\right)}}{b^{2}-a^{2}}=e^{\left(a^{2}\right)}$$ What is the ambiguity in the notation \(e^{a^{2}}\). (Consider \(4^{3^{2}}\).) Use parenthesis, they are cheap. However, common practice is to interpret \(e^{t^{2}}\) as \(e^{\left(t^{2}\right)}\).

Use the logarithm chain rule to prove that for all numbers, \(n\) : Power chain rule for all \(n \quad\left[(u(t))^{n}\right]^{\prime}=n(u(t))^{n-1} u^{\prime}(t)\) Assume that \(u\) is a positive increasing function and \(u^{\prime}(t)\) exists.

Argue that $$\lim _{b \rightarrow a} \frac{e^{\sqrt{b}}-e^{\sqrt{a}}}{\sqrt{b}-\sqrt{a}}=e^{\sqrt{a}}$$

In Section 1.3 we found from the discrete model of light extinction, \(I_{d+1}=I_{d}-0.18 I_{d}\) that the solution \(\quad I_{d+1}=0.82 I_{d}\) Light decrease in water is continuous, however. Find a value of \(k\) for which the solution to the continuous model, \(I^{\prime}(x)=-k I(x),\) matches the data.

The Body Mass Index, $$\mathrm{BMI}=\frac{\text { Mass }}{\text { Height }^{2}}$$ was introduced by Adolphe Quetelet, a French mathematician and statistician in \(1869 .\) The Center for Disease Control and Prevention (CDC) notes that BMI is a helpful indicator of overweight and obesity in adults. From simple allometric considerations, BMI3 = Mass/Height \(^{3}\) should be approximately a constant, \(C\). If \(B M I 3=\) Mass/Height \(^{3}=C\) then \(B M I=\) Mass/Height \(^{2}=C\) Height. so that BMI should increase with height. CDC also states that "... women are more likely to have a higher percentage of body fat than men for the same BMI." If a male and a female both have \(\mathrm{BMI}=23\) and are of average height for their sex \((1.77\) meters for males and 1.63 meters for females), then BMI3 for the male \(=\frac{23}{1.77}=13.0\) and BMI3 for the female \(=\frac{23}{1.63}=14.1\) Thus BMI3 is larger for the female than for the male and may indicate a larger percentage of body fat for the female. Shown are four Age, and 50 th percentile Weight, Height data points for boys and for girls. Compute BMI and BMI3 for the four points and plot the sixteen points on a graph. Which of the two indices, BMI or BMI3, remains relatively constant with age? Data are from the Centers for Disease Control and Prevention, http://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf and \(\cdots\) cj41c022.pdf. $$ \begin{array}{|l|rrrr|} \hline \text { Age (Boys) } & 8 & 12 & 16 & 20 \\ \hline \text { Weight (kg) (50 percentile) } & 26 & 41 & 62 & 71 \\ \text { Height (cm) (50 percentile) } & 128 & 149 & 174 & 177 \\ \text { BMI kg/m }^{2} & & & & \\ \text { BMI3 kg/m }^{3} & & & & \\ \hline & & & 12 & 16 & 20 \\ \text { Age (Girls) } & 26 & 41 & 54 & 58 \\ \hline \text { Weight (kg) (50 percentile) } & 128 & 151 & 162 & 163 \\ \text { Height (cm) (50 percentile) } & & & & \\ \text { BMI kg/m }^{2} & & & & \\ \text { BMI3 kg/m }^{3} & & & & \\ & & & & \\ \hline \end{array} $$ We suggest that BMI3 might be more useful than BMI as an index of body fat. Other indices of body fat that have been suggested include \(M / H, M^{1 / 3} / H, H / M^{1 / 3},\) and \(c M^{1.2} / H^{3.3}\). The interested reader should visit the web site cdc.gov/ncedphp/dnpa/bmi and read the references there.

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