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Ch.12 - Parametric and Polar Curves
Briggs - Calculus: Early Transcendentals 3rd Edition
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Tutti i libri di testoBriggs 3rd EditionCh.12 - Parametric and Polar CurvesProblema 12.3.39
Capitolo 12, Problema 12.3.39

33–40. Areas of regions Make a sketch of the region and its bounding curves. Find the area of the region.


The region inside one leaf of r = cos 3θ

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First, understand the curve given: \(r = \cos 3\theta\) is a rose curve with 3 petals because the coefficient of \(\theta\) inside the cosine is 3. Each petal corresponds to a range of \(\theta\) where \(r\) is positive.
To find the area of one leaf (one petal), identify the interval of \(\theta\) that traces out exactly one petal. Since the rose has 3 petals evenly spaced over \(0\) to \(2\pi\), one petal corresponds to an interval of length \(\frac{2\pi}{3}\). Typically, one petal is traced from \(\theta = -\frac{\pi}{6}\) to \(\theta = \frac{\pi}{6}\) or from \(0\) to \(\frac{\pi}{3}\) depending on the petal chosen.
Recall the formula for the area enclosed by a polar curve between angles \(\alpha\) and \(\beta\) is: \(\text{Area} = \frac{1}{2} \int_{\alpha}^{\beta} r^2 \, d\theta\)
Substitute \(r = \cos 3\theta\) into the formula to get: \(\text{Area} = \frac{1}{2} \int_{\alpha}^{\beta} (\cos 3\theta)^2 \, d\theta\)
Evaluate the integral by using the identity \(\cos^2 x = \frac{1 + \cos 2x}{2}\) to simplify the integrand before integrating. Then compute the definite integral over the chosen interval for one petal.

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Polar Coordinates and Graphing

Polar coordinates represent points using a radius and an angle, making it easier to describe curves like r = cos 3θ. Understanding how to sketch such curves helps visualize the region whose area is to be found, especially when the curve forms multiple 'leaves' or petals.
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05:32
Intro to Polar Coordinates

Area Calculation in Polar Coordinates

The area enclosed by a polar curve between two angles is found using the integral formula A = (1/2) ∫ (r(θ))^2 dθ. This formula accounts for the sector-like shape of regions in polar graphs, allowing precise calculation of areas bounded by curves like r = cos 3θ.
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05:32
Intro to Polar Coordinates

Determining Limits of Integration for One Leaf

To find the area of one leaf of r = cos 3θ, it is essential to identify the correct interval of θ where the leaf exists. This involves solving r = 0 to find boundary angles and integrating over the range that traces exactly one petal without overlap.
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05:50
One-Sided Limits
Pratica correlata
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77–80. Slopes of tangent lines Find all points at which the following curves have the given slope.


x = 2 cos t, y = 8 sin t; slope = -1

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Write the equations that are used to express a point with polar coordinates (r, θ) in Cartesian coordinates.

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77–80. Slopes of tangent lines Find all points at which the following curves have the given slope.


x = 2 + √t, y = 2 - 4t; slope = -8

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57–64. Graphing polar curves Graph the following equations. Use a graphing utility to check your work and produce a final graph.


r = sin 3θ

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93–94. Parametric equations of ellipses Find parametric equations (not unique) of the following ellipses (see Exercises 91–92). Graph the ellipse and find a description in terms of x and y.


An ellipse centered at (-2, -3) with major and minor axes of lengths 30 and 20, parallel to the x- and y-axes, respectively, generated counterclockwise (Hint: Shift the parametric equations.)

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37–52. Curves to parametric equations Find parametric equations for the following curves. Include an interval for the parameter values. Answers are not unique.


The horizontal line segment starting at P(8, 2) and ending at Q(−2, 2)

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