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 - 10.3 Exercises - Page 688: 57

Answer

The slope of the tangent line to the given polar curve at the point where: $\theta = \pi$ is equal to: $$-\pi$$

Work Step by Step

1. Write the formula for the slope of the tangent line: $$\frac{dy}{dx} = \frac{\frac{dr}{d\theta}sin(\theta) + rcos(\theta)}{\frac{dr}{d\theta}cos(\theta) - rsin(\theta)} $$ 2. Calculate $\frac{dr}{d\theta}$ and substitute the equation into the formula: $\frac{dr}{d\theta} = \frac{d(1/\theta)}{d\theta} = - \frac 1 {\theta^2}$ $\frac{dy}{dx} = \frac{-(\frac{1}{\theta^2})sin(\theta) + (1/\theta)cos(\theta)}{-(\frac{1}{\theta^2})cos(\theta) - (1/\theta)sin(\theta)} \div \frac{1/\theta}{1/\theta} = \frac{-(\frac{1}{\theta})sin(\theta) + cos(\theta)}{-(\frac{1}{\theta})cos(\theta) - sin(\theta)}$ 3. Calculate the slope when $\theta = \pi$ $\frac{dy}{dx} = \frac{-(1/\pi)sin(\pi) + cos(\pi)}{-(1/\pi)cos(\pi) - sin(\pi)} = \frac{-(1/\pi)(0) + (-1)}{-(1/\pi)(-1) - 0} = \frac{-1}{1/\pi} = -\pi$
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