How do you convert r(2 - cos theta) = 2r(2cosθ)=2 into a rectangular equation?

1 Answer
Apr 20, 2016

3 x^2+4 y^2-4 x -4 = 03x2+4y24x4=0

Explanation:

2 r = r cos theta + 2=x+22r=rcosθ+2=x+2.

So, 4 r^2=(x+2)^24r2=(x+2)2.
4 (x^2+y^2)=x^2+4x+44(x2+y2)=x2+4x+4
3 x^2+4 y^2-4 x -4 = 03x2+4y24x4=0

The given equation is 1/r=1-(1/2) cos theta1r=1(12)cosθ
This represents an ellipse with eccentricity e = 1/2e=12 and semi-latus rectum l = 1. Semi-major axis a = l/(1-e^2)=4/3l1e2=43.
The negative sign indicates that the initial line is reversed, from pole (a focus) to the center of the ellipse.