Math Problem Statement

Find the area A of the shaded region in the figure between the inner and outer loop of the limaçon with polar equation r = 12 cos(θ) - 6.

Solution

To find the area of the shaded region between the inner and outer loop of the limaçon, we can use the polar area formula. Given the limaçon's polar equation:

r=12cos(θ)6r = 12 \cos(\theta) - 6

we'll proceed with these steps:

  1. Identify the Inner and Outer Loops: The inner loop occurs where r=0r = 0, which gives: 12cos(θ)6=0cos(θ)=1212 \cos(\theta) - 6 = 0 \Rightarrow \cos(\theta) = \frac{1}{2} This happens at θ=π3\theta = \frac{\pi}{3} and θ=5π3\theta = \frac{5\pi}{3}.

  2. Calculate the Bounds for Integration: We will integrate from θ=0\theta = 0 to θ=π\theta = \pi, as this covers one complete sweep of both loops.

  3. Set Up the Area Formula: To find the area between the inner and outer loops, we calculate the area of the outer loop and subtract the area of the inner loop.

    The area AA between two curves in polar coordinates is given by: A=12αβ(router2rinner2)dθA = \frac{1}{2} \int_{\alpha}^{\beta} \left( r_{\text{outer}}^2 - r_{\text{inner}}^2 \right) \, d\theta

  4. Compute the Area of the Outer and Inner Loops: Since both loops are generated by the same function r=12cos(θ)6r = 12 \cos(\theta) - 6, we can calculate the total area by setting up the integral over 00 to π\pi.

Let's proceed with these calculations.

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Math Problem Analysis

Mathematical Concepts

Calculus
Polar Coordinates
Area Between Curves

Formulas

A = 1/2 ∫ (r_outer^2 - r_inner^2) dθ

Theorems

Polar Area Formula

Suitable Grade Level

Undergraduate Calculus