Area of circle in polar coordinates

In summary, the conversation discusses finding the area using polar integration, with the given equation and appropriate interval of integration being [0, pi]. The student initially gets the answer of 2pi, but later realizes their mistake of having their calculator in degree mode. It is also mentioned that the appropriate interval of integration could also be [-pi/2, pi/2].
  • #1
Malabeh

Homework Statement


r=2cos(theta) I want to find the area using polar integration.

Homework Equations


area=(1/2)r^2 from 0-pi

The Attempt at a Solution


When I plug everything in I get 2pi as the answer. I'm in multivariable calculus so this is very frustrating. What am I doing wrong, I don't know, but it's really really really really bugging me. I have an extra 2 somewhere and I don't know where.
 
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  • #2
EDIT: I don't know how to delete a post but I got it. My calculator was in degree mode.
 
  • #3
Malabeh said:
EDIT: I don't know how to delete a post but I got it. My calculator was in degree mode.
While you may have gotten the correct answer, if you plot that circle you will see that the appropriate interval of integration would be ##[-\frac \pi 2,\frac \pi 2]##, not ##[0,\pi]##.
 
  • #4
LCKurtz said:
While you may have gotten the correct answer, if you plot that circle you will see that the appropriate interval of integration would be ##[-\frac \pi 2,\frac \pi 2]##, not ##[0,\pi]##.
It works both ways, does it not?
 

1. What is the formula for finding the area of a circle in polar coordinates?

The formula for finding the area of a circle in polar coordinates is A = (1/2)r^2θ, where r is the radius of the circle and θ is the central angle in radians.

2. How do you convert rectangular coordinates to polar coordinates?

To convert rectangular coordinates (x, y) to polar coordinates (r, θ), you can use the formulas r = √(x^2 + y^2) and θ = tan^-1(y/x).

3. Can you use the Pythagorean theorem to find the area of a circle in polar coordinates?

No, the Pythagorean theorem cannot be used to find the area of a circle in polar coordinates. It can only be used for finding the distance between two points in a Cartesian coordinate system.

4. How do you find the area of a sector in polar coordinates?

To find the area of a sector in polar coordinates, you can use the formula A = (1/2)r^2θ, where r is the radius of the circle and θ is the central angle in radians. This formula is the same as finding the area of a circle, but you must first convert the central angle from degrees to radians.

5. Can you use negative values for r or θ in finding the area of a circle in polar coordinates?

No, both r and θ must be positive values in order to find the area of a circle in polar coordinates. Negative values would result in imaginary or undefined solutions.

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