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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 12.2.6

What is the polar equation of the horizontal line y = 5?

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Recall the relationship between Cartesian coordinates \((x, y)\) and polar coordinates \((r, \theta)\): \(x = r \cos{\theta}\) and \(y = r \sin{\theta}\).
Since the line is given by \(y = 5\), substitute \(y\) with \(r \sin{\theta}\) to get the equation \(r \sin{\theta} = 5\).
To express \(r\) in terms of \(\theta\), solve the equation for \(r\): \(r = \frac{5}{\sin{\theta}}\).
Note that this equation is valid for values of \(\theta\) where \(\sin{\theta} \neq 0\), which corresponds to angles where the line \(y=5\) exists in polar coordinates.
Thus, the polar equation of the horizontal line \(y=5\) is \(r = \frac{5}{\sin{\theta}}\).

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Polar Coordinates

Polar coordinates represent points 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. This system is useful for describing curves that are difficult to express in Cartesian coordinates.
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Intro to Polar Coordinates

Conversion Between Cartesian and Polar Coordinates

To convert between Cartesian (x, y) and polar (r, θ) coordinates, use the formulas x = r cos θ and y = r sin θ. Conversely, r = √(x² + y²) and θ = arctan(y/x). These relationships allow expressing Cartesian equations in terms of r and θ.
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Intro to Polar Coordinates

Equation of a Horizontal Line in Polar Form

A horizontal line y = c can be expressed in polar coordinates by substituting y = r sin θ. Thus, the equation becomes r sin θ = c. This form relates the radius and angle for all points on the horizontal line.
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Percorso guidato
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Equations of Tangent Lines