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Ch.12 - Parametric and Polar Curves
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 12, Problem 12.2.30

25–30. Converting coordinates Express the following polar coordinates in Cartesian coordinates.


(4, 5π)

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Recall the formulas to convert polar coordinates \((r, \theta)\) to Cartesian coordinates \((x, y)\): \(x = r \cos(\theta)\) \(y = r \sin(\theta)\)
Identify the given polar coordinates: \(r = 4\) and \(\theta = 5\pi\).
Substitute the values into the conversion formulas: \(x = 4 \cos(5\pi)\) \(y = 4 \sin(5\pi)\)
Use the periodic properties of trigonometric functions to simplify \(\cos(5\pi)\) and \(\sin(5\pi)\). Remember that \(\cos(\theta)\) and \(\sin(\theta)\) have periods of \(2\pi\).
Calculate the simplified values of \(x\) and \(y\) to express the Cartesian coordinates corresponding to the given polar coordinates.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polar Coordinates

Polar coordinates represent a point in the plane using a radius and an angle, denoted as (r, θ), where r is the distance from the origin and θ is the angle measured from the positive x-axis. Understanding this system is essential for converting to Cartesian coordinates.
Recommended video:
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Intro to Polar Coordinates

Conversion Formulas from Polar to Cartesian

To convert polar coordinates (r, θ) to Cartesian coordinates (x, y), use the formulas x = r cos(θ) and y = r sin(θ). These formulas translate the radius and angle into horizontal and vertical distances on the Cartesian plane.
Recommended video:
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Convert Equations from Rectangular to Polar

Angle Measurement and Trigonometric Values

Angles in polar coordinates are often given in radians. Knowing how to evaluate trigonometric functions like sine and cosine at specific angles, such as multiples of π, is crucial for accurate conversion to Cartesian coordinates.
Recommended video:
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Introduction to Trigonometric Functions
Related Practice
Textbook Question

53–56. Circular motion Find parametric equations that describe the circular path of the following objects. For Exercises 53–55, assume (x, y) denotes the position of the object relative to the origin at the center of the circle. Use the units of time specified in the problem. There are many ways to describe any circle.


A bicyclist rides counterclockwise with constant speed around a circular velodrome track with a radius of 50 m, completing one lap in 24 seconds.

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Textbook Question

39–50. Equations of ellipses and hyperbolas Find an equation of the following ellipses and hyperbolas, assuming the center is at the origin. 


A hyperbola with vertices (±4, 0) and foci (±6, 0)

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Textbook Question

Second derivative Assume a curve is given by the parametric equations x=f(t) and y=g(t), where f and g are twice differentiable. Use the Chain Rule to show that y″x=(fʹ(t)g″(t)−gʹ(t)f″(t))/(fʹ(t))³.  

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Textbook Question

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


r² = 4 sin θ  

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Textbook Question

Air drop—inverse problem A plane traveling horizontally at 100 m/s over flat ground at an elevation of 4000 m must drop an emergency packet on a target on the ground. The trajectory of the packet is given by

x = 100t, y = −4.9t² + 4000, t ≥ 0

where the origin is the point on the ground directly beneath the plane at the moment of the release. How many horizontal meters before the target should the packet be released in order to hit the target?

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Textbook Question

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


{Use of Tech} The complete limaçon r=4−2cosθ

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