Polar Regions: Area, Arc Length, and Surface Area

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SUMMARY

The discussion focuses on calculating the area, arc length, and surface area of a polar graph defined by the equation r = 1 + 2cos(Θ). The integrals required for these calculations are established: the area A is determined using A = ∫(1/2)(f(Θ))² dΘ, while the arc length AL is calculated with AL = ∫√(r² + (dr/dΘ)²) dΘ. The user seeks clarification on the bounds for the integrals, particularly for the area of the large loop, which spans from 4π/3 to 2π/3. The discussion highlights the importance of correctly identifying integral limits to accurately compute the desired values.

PREREQUISITES
  • Understanding of polar coordinates and their graphical representation
  • Familiarity with integral calculus, specifically in polar form
  • Knowledge of the equations for area and arc length in polar coordinates
  • Ability to determine integral bounds based on polar graph behavior
NEXT STEPS
  • Study the derivation and application of the area formula A = ∫(1/2)(f(Θ))² dΘ in polar coordinates
  • Learn how to compute arc length using AL = ∫√(r² + (dr/dΘ)²) dΘ
  • Research methods for finding surface area of solids of revolution in polar coordinates
  • Explore examples of polar graphs to practice setting integral bounds for various shapes
USEFUL FOR

Students studying calculus, particularly those focusing on polar coordinates and integral applications, as well as educators seeking to enhance their teaching of these concepts.

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Homework Statement



Consider the graph (see attachment) of r = 1 +2cos[tex]\Theta[/tex] in polar coordinates. SET UP integrals to find
1. the area inside the large loop minus the area of the small loop.
2. the arc length of the small loop
3. the surface area of the surface formed by revolving the large loop about the initial ray.


Homework Equations



area A of the polar region
A = [tex]\int[/tex][tex]\frac{1}{2}[/tex](f([tex]\Theta[/tex]))[tex]^{2}[/tex]d[tex]\Theta[/tex] with upper limit b and lower limit a.

arc length AL of the polar region:
AL = [tex]\int[/tex][tex]\sqrt{r^{2}+(\frac{dr}{d\Theta})^{2}} d\Theta[/tex] with upper limit b and lower limit a.

not sure what equation i need to figure out the surface area one

The Attempt at a Solution



I'm pretty much lost when it comes to the entire problem, and have no ideas where to start. Please help!
 

Attachments

  • Calc Graph.jpg
    Calc Graph.jpg
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You've got the equations right. You just have to figure out what to use for the bounds. For 1, if you want to encompass only the larger arc, what should the upper bound be?
 
Well if the 4π/3 ray moved in a counterclockwise motion until the 2π/3 ray, then the ray would sweep the entire area of the large loop. But that would mean doing an integral from a lower bound of 4π/3 to the upper bound of 2π/3. This to me doesn't seem right since usually the lower bound is smaller than the upper bound.
 

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