# Find the locus of a pt in polar form

1. Nov 3, 2012

### VHAHAHA

the question is showed below
i know that x=rcos θ and y= rsinθ and x^2 + y^2 = R^2
but i just dun know how to find the locus is polar form
any clue ?

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2. Nov 3, 2012

### AJ Bentley

All you have to do is to find the position of the ring in terms of r and θ.
It's easy to get r in terms of t and also θ in terms of t.

That gives you two formulae - you just have to eliminate 't' between them.

3. Nov 3, 2012

### VHAHAHA

u mean

r= (u)t
and
θ= (w)t

so
rw=uθ and then rw-uθ=0 ??

actually i have listed this equ but i just don't believe my self
i feel that i have missed something

4. Nov 3, 2012

### AJ Bentley

Ya gotta have faith.

If you're not sure, draw the locus (path).
Note that rω = θu can be written as r = kθ where k is a constant - that's easy to plot.

5. Nov 3, 2012

### VHAHAHA

the path will be something like a @ ??

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6. Nov 3, 2012

7. Nov 3, 2012

### VHAHAHA

ya i got it, thx