Mathematics

Mathematics

Problem

Let nn be a positive integer. Derive a closed-form expression for the exact area of one petal of the curve r=asin⁡(nθ)r = a\sin(n\theta) in terms of aa and nn.
Intuitive explanation

The key is recognizing that a petal of r=asin⁡(nθ)r = a\sin(n\theta) traces out when rr goes from 0 to its maximum and back to 0 as θ\theta sweeps through one complete cycle. Use the polar area formula A=12∫r2 dθA = \frac{1}{2}\int r^2 \, d\theta over the angular interval for a single petal, then exploit the symmetry and periodicity of the sine function to simplify the integral into a standard form you can evaluate.

Intuitive explanation

The key is recognizing that a petal of r=asin⁡(nθ)r = a\sin(n\theta) traces out when rr goes from 0 to its maximum and back to 0 as θ\theta sweeps through one complete cycle. Use the polar area formula A=12∫r2 dθA = \frac{1}{2}\int r^2 \, d\theta over the angular interval for a single petal, then exploit the symmetry and periodicity of the sine function to simplify the integral into a standard form you can evaluate.

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