Converting Cartesian to Polar: Finding the Polar Equation

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In summary, the task is to find a polar equation for a Cartesian equation, specifically y = 1 + 3x. The equations provided are x^2 + y^2 = r^2, x = Rcos(θ), and y = Rsin(θ). The attempt at a solution involved squaring the Cartesian equation, which would not result in the original equation. The correct approach is to replace x and y with polar coordinates, rcos(θ) and rsin(θ), respectively. This will give a polar equation for the curve.
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ThiagoG
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Homework Statement


Find a polar equation for the curve represented by the Cartesian equation.

y=1+3x

Homework Equations


x2+y2=r2
x=Rcos(θ)
y=Rsin(θ)

The Attempt at a Solution


(1+3x)2+x2=r2
1+6x+10x2=r2
1+6rcos(θ)+10r2cos2(Θ)=r2
 
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  • #2
Why are you squaring? This will give you a relation between [itex]x^2[/itex] and [itex]y^2[/itex], not x and y, and so not the original equation. Just replace "x" with [itex]r cos(\theta)[/itex] and "y" with [itex]r sin(\theta)[/itex] in the original equations.
 
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  • #3
HallsofIvy said:
Why are you squaring? This will give you a relation between [itex]x^2[/itex] and [itex]y^2[/itex], not x and y, and so not the original equation. Just replace "x" with [itex]r cos(\theta)[/itex] and "y" with [itex]r sin(\theta)[/itex] in the original equations.

Oh thank makes a lot of sense. Thank you.
 

What is a polar equation?

A polar equation is a mathematical expression that describes a curve or shape in polar coordinates, where a point is represented by its distance from the origin and its angle with respect to a fixed direction.

How do you convert a Cartesian equation to a polar equation?

To convert a Cartesian equation to a polar equation, you can use the following substitutions: x = r cosθ and y = r sinθ. Once you have substituted these values, you can rearrange the equation to solve for r in terms of θ.

What does the value of r represent in a polar equation?

The value of r in a polar equation represents the distance from the origin to a point on the curve, also known as the radius. This distance is measured in the same units as the x and y axes in a Cartesian coordinate system.

How do you graph a polar equation?

To graph a polar equation, you can plot points by substituting different values of θ into the equation and calculating the corresponding values of r. These points can then be connected to create a curve. You can also use a graphing calculator to plot the equation.

What are some common polar equations?

Some common polar equations include circles, cardioids, roses, limaçons, lemniscates, and spirals. These equations can have different forms and parameters, but they all follow the same basic principles of polar coordinates.

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