# Converting Spherical to Cartesian

Problem solved!

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Mark44
Mentor
Your equation is equivalent to $\rho$ = cos($\phi$)/(1 - cos2($\phi$).

Your relevant equations show the converstion from spherical to Cartesian coordinates. Do you know the conversions going in the other direction?

One trick that will be helpful is to multiply both sides by rho. This potentially adds a point (rho = 0) that might not be a solution of your original equation, so you should check whether this is already a solution of your equation.

Solved!

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Mark44
Mentor
As an intermediate step, look at what I have in my previous post. Use trig identities to get to what I showed, then go from there.

vela
Staff Emeritus
Homework Helper
Look at the equations for x, y, and z. Note that they're all of the form rho times some combination of sines and cosines. So the first thing you should do is rewrite everything in terms of sines and cosines. Next, rearrange terms so the trig functions multiply rho. If needed, do as Mark suggested, and multiply both sides by rho. Then try to identify what cartesian coordinates the various products are equal to.

Solved!

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Mark44
Mentor
You're missing a factor of cos(phi) in the numerator on the right side.

Solved!

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vela
Staff Emeritus
Homework Helper
Try bringing the (1+cos^2(phi)) to the other side.

Mark44
Mentor
I dont think so, because doesnt pcos(phi)=z?
OK. I didn't catch what you were doing.

vela said:
Try bringing the (1+cos^2(phi)) to the other side.
Don't you mean (1 - cos^2(phi))?

Mark44
Mentor
bglb212 said:
x^2+y^2+z^2=z/(1-cos(phi)^2
It's probably helpful not to change the rho^2 on the left side just yet.

Solved!

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Mark44
Mentor
Let us decide whether nothing good comes out of it. Show us what you tried.

You have rho^2 = z/(1 - cos^2(phi))
What do you get when you multiply both sides by 1 - cos^2(phi)?

Solved!

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vela
Staff Emeritus
Homework Helper
Don't you mean (1 - cos^2(phi))?
Yes, I did. Thanks for catching that.

Mark44
Mentor
got it, I like you mark. you're helpful. may your children be plentiful and live long
That's a very nice thing to say! Thank you!

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Mark44
Mentor
csc(x) = 1/sin(x), cot(x) = cos(x)/sin(x)

Are those the ones you mean?

Evo
Mentor
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