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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.R.36a

Polar conversion Consider the equation r=4/(sinθ+cosθ). 


a. Convert the equation to Cartesian coordinates and identify the curve it describes.  

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1
Recall the relationships between polar and Cartesian coordinates: \(x = r \cos\theta\), \(y = r \sin\theta\), and \(r = \sqrt{x^2 + y^2}\).
Start with the given polar equation: \(r = \frac{4}{\sin\theta + \cos\theta}\).
Multiply both sides of the equation by \((\sin\theta + \cos\theta)\) to get: \(r (\sin\theta + \cos\theta) = 4\).
Substitute \(r \sin\theta = y\) and \(r \cos\theta = x\) into the equation, yielding \(y + x = 4\).
Recognize that the equation \(x + y = 4\) is a linear equation representing a straight line in Cartesian coordinates.

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Polar to Cartesian Coordinate Conversion

This involves translating equations from polar form (r, θ) to Cartesian form (x, y) using the relationships x = r cosθ and y = r sinθ. Understanding these conversions allows one to rewrite polar equations in terms of x and y, facilitating analysis using familiar Cartesian methods.
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Intro to Polar Coordinates

Trigonometric Identities and Manipulation

Trigonometric identities, such as expressing sinθ and cosθ in terms of x and y, or using sum formulas, are essential for simplifying and rearranging equations during conversion. Mastery of these identities helps in isolating variables and recognizing standard curve forms.
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Verifying Trig Equations as Identities

Identification of Conic Sections

After converting to Cartesian form, recognizing the resulting equation as a conic section (circle, ellipse, parabola, or hyperbola) is crucial. This involves comparing the equation to standard forms and understanding geometric properties to classify the curve accurately.
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Parabolas as Conic Sections