Originally Posted by

**mdunnbass** Hi everyone,

This is my first post here, so please feel free to ignore/delete/relocate this post if it is in the wrong place or has been covered before.

I was idly wondering about this the other day, and thought I would seek out the insight of those who might know.

If we take a Unit circle, with it's center located at the origin and radius r=1, the equation of the circle is written as

cos^2(theta) + sin^2(theta) = 1

where theta is defined as angle POR, where P is a point on the circle, O is the origin, and R is, for the sake of simplicity, (x = 1, y = 0)

Is there a simple way to write the equation of the same circle, with respect to a different angle, phi, defined as PQR, where Q is any random point along y=0, such as (x=-0.5, y=0)?

I have been trying to figure it out in terms of generating triangle POQ, and invoking the laws of sines and cosines, but I inevitably going in circles (pun not intended) and wind up with something along the lines of x = x.

Any insights would be greatly appreciated.

Thanks,

Matt