Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 10 - Parametric Equations and Polar Coordinates - 10.2 Exercises - Page 676: 60

Answer

$$S = \int_{0}^{1} 2\pi (t + t^4) \sqrt {1 + 4t^2 -4t^3 + 9t^4 + 16t^6} \space dt \approx 12.7176$$

Work Step by Step

1. Write the formula for the area of the surface obtained by rotating a curve about the $x$-axis. $$S = \int_{\alpha}^{\beta} 2\pi y \sqrt {(\frac{dx}{dt})^2 + (\frac{dy}{dt})^2} \space dt$$ 2. Calculate: $\frac{dx}{dt}$ and $\frac{dy}{dt}$: $\frac{dx}{dt} = \frac{d(t^2 - t^3)}{dt} = 2t -3t^2$ $\frac{dy}{dt} = \frac{d(t + t^4)}{dt} = 1 + 4t^3 $ 3. Substitute the given values into the formula: $S = \int_{0}^{1} 2\pi (t + t^4) \sqrt {(2t - 3t^2)^2 + (1 + 4t^3)^2} \space dt$ $S = \int_{0}^{1} 2\pi (t + t^4) \sqrt {(4t^2 -12t^3 + 9t^4) + (1 + 8t^3 +16t^6)} \space dt$ $S = \int_{0}^{1} 2\pi (t + t^4) \sqrt {1 + 4t^2 -4t^3 + 9t^4 + 16t^6} \space dt$ 4. Write that integral on your calculator (you can use an online one). The result is: $S \approx 12.7176$
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