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Recall that when a curve is given in polar
coordinates r = f(θ) for a ≤ θ ≤ b,
the arc length of a polar curve is determined as follows:
For the given function r = 100cos2θ for 0 ≤ θ ≤ π/2,
the derivative dr/dθ is given by
The arc length of the ski track is determined as:
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n |
θ |
f(θ) |
0 |
0 |
1.00 |
1 |
π/20 |
1.13 |
2 |
π/10 |
1.43 |
3 |
3π/20 |
1.72 |
4 |
π/5 |
1.93 |
5 |
π/4 |
2.00 |
6 |
3π/10 |
1.93 |
7 |
7π/20 |
1.72 |
8 |
2π/5 |
1.43 |
9 |
9π/20 |
1.13 |
10 |
π/2 |
1.00 |
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Since there is no obvious technique to perform the integration, Simpson's
Rule is used. According to the Simpson's Rule, an integration can be approximated as,
where n is even and Δθ = (b - a)/n.
In this case, , n = 10, and Δθ = (π/2)/10 = π/20.
The values of f(θ) subject to different values of θ are summarized in the table on the left.
The integration can then be evaluated to give the length of the ski track as
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