All Flashcards

Area of a sector in polar coordinates?

$A = \frac{1}{2}r^2\theta$

Area enclosed by polar curve $r = f(\theta)$ from $a$ to $b$ ?

$A = \frac{1}{2}\int_{a}^{b}[f(\theta)]^2 d\theta$

Half-angle identity for $\cos^2(\theta)$ ?

$\cos^2(\theta) = \frac{1 + \cos(2\theta)}{2}$

Area of one petal of a rose curve?

$A = \frac{1}{2}\int_{a}^{b} [f(\theta)]^2 d\theta$ , where the limits a and b define one petal.

Why use polar coordinates for certain curves?

Easier to describe curves like circles and spirals than Cartesian coordinates.

Explain the concept of integrating in polar coordinates to find area.

Summing infinitely small sectors (pizza slices) to find the total area enclosed by the curve.

How does symmetry simplify area calculations in polar coordinates?

Calculate the area of one symmetric portion and multiply to get the total area.

Why is the area formula $\frac{1}{2}\int_{a}^{b}r^2 d\theta$ ?

It sums the areas of infinitesimal sectors with radius $r$ and angle $d\theta$ .

What does the integral $\int_{a}^{b} r d\theta$ represent in polar coordinates?

It does not directly represent area; the correct area integral is $\frac{1}{2}\int_{a}^{b} r^2 d\theta$ .

Steps to find area inside $r = 2\cos(\theta)$ from $0$ to $\pi$ ?

Set up: $A = \frac{1}{2}\int_{0}^{\pi}(2\cos(\theta))^2 d\theta$ . 2. Simplify. 3. Integrate and evaluate.

Steps to find area of one petal of $r = \sin(2\theta)$ ?

Find range for one petal (e.g., $0$ to $\frac{\pi}{2}$ ). 2. Set up integral: $A = \frac{1}{2}\int_{0}^{\frac{\pi}{2}}(\sin(2\theta))^2 d\theta$ . 3. Integrate.

How to find the area of a polar curve when symmetry is present?

Identify symmetry. 2. Find the limits of integration for one symmetrical part. 3. Integrate and multiply by the appropriate factor.

Steps to calculate area enclosed by $r=3+3\sin(\theta)$ ?

Sketch. 2. Recognize symmetry. 3. Set up integral: $A = \frac{1}{2}\int_{0}^{2\pi}(3+3\sin(\theta))^2 d\theta$ . 4. Simplify and solve.

How to deal with $\sin^2(\theta)$ or $\cos^2(\theta)$ in polar area integrals?

Use the half-angle identities: $\cos^2(\theta) = \frac{1 + \cos(2\theta)}{2}$ and $\sin^2(\theta) = \frac{1 - \cos(2\theta)}{2}$ .

What is the first step in finding the area enclosed by a polar curve?

Sketch the curve to understand its shape and any symmetries.