Chapter 30: Problem 34
Solve the given problems. Find the approximate area bounded by \(y=\sin x, y=0,\) and \(x=\pi / 6\) by using two terms of the expansion for \(\sin x .\) Compare the result with that found by direct integration.
Short Answer
Expert verified
Approximate area is \( \frac{\pi^2}{72} - \frac{\pi^4}{31104} \); exact area is \(1 - \frac{\sqrt{3}}{2}\).
Step by step solution
01
Use the Taylor Series Expansion
To approximate the area, we first express \( \sin x \) using its Taylor series expansion up to two terms. The Taylor series for \( \sin x \) is given by \( \sin x = x - \frac{x^3}{3!} + \cdots \). By choosing two terms, we have: \( \sin x \approx x - \frac{x^3}{6} \).
02
Set Up the Integral for Approximation
The area bounded by \( y = \sin x \) and \( y = 0 \) from \( x = 0 \) to \( x = \pi/6 \) is represented by the integral \( \int_0^{\pi/6} \sin x \, dx \). Using the approximation from the Taylor series (\( x - \frac{x^3}{6} \)), the integral becomes: \[ \int_0^{\pi/6} \left( x - \frac{x^3}{6} \right) \, dx. \]
03
Evaluate the Approximate Integral
Perform the integration: \( \int \left( x - \frac{x^3}{6} \right) \, dx = \frac{x^2}{2} - \frac{x^4}{24} + C \). Evaluating this from 0 to \( \pi/6 \) gives: \[ \left[ \frac{x^2}{2} - \frac{x^4}{24} \right]_0^{\pi/6} = \frac{(\pi/6)^2}{2} - \frac{(\pi/6)^4}{24}. \] Simplifying, we find: \[ \text{Approximate Area} = \frac{\pi^2}{72} - \frac{\pi^4}{31104}. \]
04
Setup the Exact Integral for Comparison
Now, calculate the exact area using \( \sin x \) directly: \( \int_0^{\pi/6} \sin x \, dx \). This integral can be evaluated to give: \[ \left[ -\cos x \right]_0^{\pi/6} = -\cos\left( \frac{\pi}{6} \right) + \cos(0). \]
05
Evaluate the Exact Integral
Substitute the values: \( -\cos\left( \frac{\pi}{6} \right) = -\frac{\sqrt{3}}{2} \) and \( \cos(0) = 1 \) gives the exact area as: \[ 1 - \frac{\sqrt{3}}{2}. \]
06
Compare Results
Compare the approximate area \( \frac{\pi^2}{72} - \frac{\pi^4}{31104} \) with the exact area \( 1 - \frac{\sqrt{3}}{2} \). The approximate value can be computed numerically and compared to the exact value for precision analysis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Taylor series
The Taylor series is a powerful tool in calculus used to approximate functions using polynomials. It's particularly handy for trigonometric functions such as \( \sin x \). The basic idea is to express a function as an infinite sum of terms calculated from the values of its derivatives at a single point. However, often we use only the first few terms to simplify calculations. For \( \sin x \), the Taylor series expansion at \( x = 0 \) is:
- \( \sin x = x - \frac{x^3}{3!} + \frac{x^5}{5!} - \cdots \)
approximate integration
Approximate integration is a method used when calculating a definite integral directly is too complex or when an exact solution is unnecessary. Through this method, we use a simpler function that closely resembles the function we wish to integrate. In this case, we turn to the Taylor series to help us modify \( \sin x \) into the more manageable expression \( x - \frac{x^3}{6} \).By replacing the function in the integral \( \int_0^{\pi/6} \sin x \, dx \) with its approximation, we get:
- \( \int_0^{\pi/6} \left( x - \frac{x^3}{6} \right) \, dx \)
trigonometric functions
Trigonometric functions are fundamental in mathematics and appear frequently in calculations involving oscillations, waves, and circular motion. Among these, the sine function, \( \sin x \), is crucial for understanding periodic phenomena.The sine function maps angles to their corresponding coordinate on a unit circle, and it is periodic, repeating every \( 2\pi \) radians. Understanding its behavior is essential in integrating functions like \( \sin x \). You can express \( \sin x \) in many ways:
- Using exact trigonometric values
- Approximate using Taylor or other polynomial series
definite integral evaluation
A definite integral represents the area under a curve, stretched along a given interval. In this exercise, we evaluated the integral \( \int_0^{\pi/6} \sin x \, dx \) to find the area enclosed by \( y = \sin x \), \( y = 0 \), and \( x = \pi/6 \).When performing definite integral evaluation directly, we utilize antiderivatives. For \( \sin x \), the antiderivative is \( -\cos x \). Hence, the evaluation from 0 to \( \pi/6 \) is as follows:
- \( \left[ -\cos x \right]_0^{\pi/6} = -\cos\left( \frac{\pi}{6} \right) + \cos(0) \)