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: 60

Answer

The slope of the tangent line to the given polar curve at that point is equal to: $$\frac{\sqrt 3}{9}$$

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: $\frac{dr}{d\theta} = \frac{d(1 + 2cos(\theta))}{d\theta} = -2sin(\theta)$ $\frac{dy}{dx} = \frac{-2sin(\theta)sin(\theta) + (1 + 2cos(\theta))cos(\theta)}{-2sin(\theta)cos(\theta) - (1 + 2cos(\theta))sin(\theta)} = \frac{-2sin^2(\theta) + cos(\theta) + 2cos^2(\theta)}{-2sin(\theta)cos(\theta) - sin(\theta) -2cos(\theta)sin(\theta)}$ $\frac{dy}{dx} = \frac{2cos(2\theta) + cos(\theta)}{-2sin(2\theta) - sin(\theta)}$ 3. Calculate the slope when $\theta = \pi/3$ $\frac{dy}{dx} = \frac{2cos(2\frac{\pi}{3}) + cos(\frac{\pi}{3})}{-2sin(2\frac{\pi}{3}) - sin(\frac{\pi}{3})} = \frac{2(-1/2) + 1/2}{-2(\frac{\sqrt 3}{2}) - \frac{\sqrt 3}{2}}$ $\frac{dy}{dx} = \frac{-1/2}{-\sqrt 3 - \frac{\sqrt 3}{2}} = \frac{-1/2}{-\frac{3\sqrt 3}{2}} = \frac{1}{3\sqrt 3} \times \frac{\sqrt 3}{\sqrt 3} = \frac{\sqrt 3}{3\sqrt 3 \sqrt 3} = \frac{\sqrt 3}{9}$
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