# Homework Help: Triple integral in polar coordinate

1. Jul 9, 2016

1. The problem statement, all variables and given/known data
why x is p(cosθ)(sinφ) ? and y=p(sinθ)(cosφ)?
z=p(cosφ)

As we can see, φ is not the angle between p and z .......

2. Relevant equations

3. The attempt at a solution

2. Jul 9, 2016

### Mr-R

Why would you think that?
Well, as I see it, $\phi$ is the angle between $z$ and $\rho$.

3. Jul 9, 2016

really? then where is p?
P is on the same line as x-axis, am i right?

4. Jul 9, 2016

### Mr-R

Nope it is not on the same axis as x. If that was the case then the equation $x^2+y^2+z^2=\rho^2$ wouldn't make sense.
If you are bothered by the provided diagram then just look up another one from another source

5. Jul 9, 2016

### ehild

6. Jul 10, 2016

### Irene Kaminkowa

You had better start from 2D - the polar coordinates, trying to understand, why x = ρ cos Θ and y = ρ sin Θ.

7. Jul 10, 2016

### vela

Staff Emeritus
That's a really bad figure. No wonder you're confused. Check out the page ehild linked to.

By the way, $\rho$ is the Greek letter rho. It's not P nor p.

8. Jul 26, 2016

### BvU

Can I also point out that physicists use $\theta$ for the polar angle and $\phi$ for the azimuthal angle ?
Much more consistent with the cylindrical $(\rho,\phi,z)$ coordinate system

So: stay alert to avoid miscommunication !