How do you convert x=3 to polar form?

2 Answers
Feb 11, 2016

Oddly enough the point (3,0)(3,0) in polar coordinates is still (3,0)(3,0)!

Explanation:

This is a somewhat incomplete question.
Do you mean express the point written in Cartesian coordinates as x=3 y=0 or (3,0) in polar coordinates or the vertical line x=3 as a polar function?

I'm going to assume the simpler case.
Expressing (3,0) in polar coordinates.
polar coordinates are written in the form (r, \theta) (r,θ) were rr is the straight line distance back to the origin and \thetaθ is the angle of the point, in either degrees or radians.

The distance from (3,0) to the origin at ( 0,0) is 3.
The positive x-axis is normally treated as being 0^o0o /00 radians ( or 360^o360o/ 2 \pi2π radians).
Formally this is because the arctan (0/3)=0arctan(03)=0 radians or 0^o0o (depending on what mode your calculator is in).
Recall, arctanarctan is just tantan backwards.
Thus (3,0)(3,0) in polar coordinates is also (3,0)(3,0) or (3,0^o)(3,0o)

Feb 11, 2016

It can be expressed:

r cos theta = 3rcosθ=3

Or if you prefer:

r = 3 sec thetar=3secθ

Explanation:

To convert an equation in rectangular form to polar form you can substitute:

x = r cos thetax=rcosθ

y = r sin thetay=rsinθ

In our example x = 3x=3 becomes r cos theta = 3rcosθ=3

If you divide both sides by cos thetacosθ then you get:

r = 3/cos theta = 3 sec thetar=3cosθ=3secθ