Calculating Arc Length in Polar Coordinates

In summary, the problem is to find the length of r=sin³(x/3) for 0<x<3pi/2. The solution involves finding the derivative of r, which is r'=cos(x/3)sin²(x/3), and using the formula for the integral of radical (r'²+r²)dx. The key to solving the problem is recognizing that sin³(x/3) can be rewritten as sin²(x/3)sin^4(x/3), and using the identity sin²(x) = (1-cos2x)/2.
  • #1
JosephR
11
0

Homework Statement



Find The length of r=sin³(x/3) 0<x<3pi/2

2. The attempt at a solution

well first i found r'=3.cos(x/3).1/3.sin²(x/3)=cos(x/3)sin²(x/3)
r²=cos²(x/3)sin^4(x/3)

then i put the formula

integral of radical (r'²+r²)dx and I'm stuck here

any help?
 
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  • #2
JosephR said:
Find The length of r=sin³(x/3) 0<x<3pi/2

well first i found r'=3.cos(x/3).1/3.sin²(x/3)=cos(x/3)sin²(x/3)
r²=cos²(x/3)sin^4(x/3)

then i put the formula

integral of radical (r'²+r²)dx and I'm stuck here

any help?

Hi JosephR! :smile:

Hint: sin6(x/3) = sin²(x/3)sin^4(x/3) :wink:
 
  • #3
hey tiny-tim:)

i knew this but it would take some time to be solved !

because sin²(x/3)=[1-cos(2x/3)]/2

anyway thanks buddy !
 

1. What are polar coordinates?

Polar coordinates are a system of coordinates used to describe the position or location of a point in a two-dimensional plane. They are represented by a distance from the origin and an angle from a reference direction, typically the positive x-axis.

2. How is arc length calculated in polar coordinates?

Arc length in polar coordinates is calculated using the formula L = ∫√(r² + (dr/dθ)²) dθ, where r is the radius and dr/dθ is the derivative of the radius with respect to the angle θ. This integral represents the distance along the curve from one point to another.

3. What is the significance of arc length in polar coordinates?

Arc length is important in polar coordinates as it allows us to calculate the length of a curve or a portion of a curve. This is useful in various applications such as calculating the distance traveled by an object moving along a curved path or determining the perimeter of a polar curve.

4. How do you find the arc length of a specific polar curve?

To find the arc length of a specific polar curve, you can use the formula L = ∫√(r² + (dr/dθ)²) dθ, where r is the equation of the curve in terms of polar coordinates. You would then integrate this expression over the desired interval of the angle θ.

5. Can polar coordinates be converted to Cartesian coordinates?

Yes, polar coordinates can be converted to Cartesian coordinates and vice versa. To convert from polar to Cartesian coordinates, we use the equations x = rcos(θ) and y = rsin(θ), where r is the distance from the origin and θ is the angle from the reference direction. To convert from Cartesian to polar coordinates, we use the equations r = √(x² + y²) and θ = tan⁻¹(y/x).

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