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Ch.12 - Parametric and Polar Curves
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 12, Problema 12.3.65

63–74. Arc length of polar curves Find the length of the following polar curves.


The spiral r = θ², for 0 ≤ θ ≤ 2π

Guida verificata passo dopo passo
1
Recall the formula for the arc length \( L \) of a curve given in polar coordinates \( r = r(\theta) \) from \( \theta = a \) to \( \theta = b \): \[ L = \int_{a}^{b} \sqrt{r(\theta)^2 + \left(\frac{d}{d\theta}r(\theta)\right)^2} \, d\theta \]
Identify the given function and interval: here, \( r(\theta) = \theta^2 \) and \( \theta \) ranges from 0 to \( 2\pi \).
Compute the derivative of \( r(\theta) \) with respect to \( \theta \): \[ \frac{d}{d\theta}r(\theta) = \frac{d}{d\theta}(\theta^2) = 2\theta \]
Substitute \( r(\theta) \) and its derivative into the arc length formula to get the integrand: \[ \sqrt{(\theta^2)^2 + (2\theta)^2} = \sqrt{\theta^4 + 4\theta^2} \]
Set up the integral for the arc length: \[ L = \int_0^{2\pi} \sqrt{\theta^4 + 4\theta^2} \, d\theta \] This integral can then be evaluated (using appropriate methods) to find the length of the spiral.

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Polar Coordinates and Curves

Polar coordinates represent points in the plane using a radius and an angle (r, θ). Polar curves are defined by equations relating r and θ, such as r = θ². Understanding how to interpret and plot these curves is essential for analyzing their properties, including length.
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Intro to Polar Coordinates

Arc Length Formula for Polar Curves

The arc length of a polar curve r(θ) from θ = a to θ = b is given by the integral ∫ₐᵇ √[r(θ)² + (dr/dθ)²] dθ. This formula accounts for changes in both radius and angle, allowing calculation of the curve's length by integrating over the specified interval.
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Percorso guidato
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Arc Length of Parametric Curves

Differentiation of Polar Functions

To apply the arc length formula, you must compute the derivative dr/dθ of the polar function r(θ). This involves differentiating r = θ² with respect to θ, which yields dr/dθ = 2θ. Accurate differentiation is crucial for correctly evaluating the integral for arc length.
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Intro to Polar Coordinates