# Polar coordinates

## Homework Statement

Hi, I have the coordinates of an "expression" for a point in a cartesian coordinate system. I'm trying to write it in a polar coordiante system (in function of r and theta) but I don't know how to find the answer

a = y-component of the point
b = x-component of the point
theta = angle between the y-axis and a line connecting the point with the origin
r = distance from the origin till the point

## Homework Equations

the expression which I would like to write in a polar coordinate system is:

a.sin(theta) + b.cos(theta)

The result should be:

r.sin(theta).cos(theta)

How to get to this result?

## Answers and Replies

Start off drawing your unit circle. You should be able to figure it out from there. If you can't figure out the transform, trying looking up coordinate transforms on wikipedia. I know they have a good page on the topic.

If you have a problem understanding where the transforms come from or how to use them, try going over some examples in a text book or drawing the vectors. This is something one really needs to understand to perform well in physics.