Is the second equation a sphere?

In summary, the first equation is easily converted to the equation of a sphere in Cartesian coordinates, while the second equation is not a sphere due to the out of phase nature of sinφ and cosθ. It is likely a quartic equation when simplified.
  • #1
gnome
1,041
1
This equation of a sphere in spherical coordinate form:
ρ = 4sinφcosθ converts very readily to (x-2)2 + y2 + z2 = 4 with very little effort.

Now this similar equation looks to me like it should also be a sphere, but I can't seem to get anywhere with it:
ρ = 4sinθcosφ

I just end up with a very ugly
x2 + y2 + z2 = 4yz/(√(x2+y2)
and I have no idea what to do with that.

Is this a dead end? Is the second equation not a sphere?
 
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  • #2
I can only ask what makes you think the second equation would be a sphere. Spherical coordinates are not "symmetric" in θ and φ.
 
  • #3
I guess I can only plead insanity on this one.

When it comes to spherical coordinates I'm an absolute greenhorn. The only reason I thought it might be a sphere is that I thought that was the equation that was given on my calc 3 exam last night, and I guess I was "mis-remembering".

But actually, I did wake up this morning thinking that the 2nd equation probably isn't a sphere; I realized that the sinφ and cosθ are "out of phase", i.e. φ is approaching its max when θ is approaching its min, and I was going to post that as a "supplementary" question. So thanks for answering my second question before I even asked it.

And thanks for pointing out so succinctly what characterizes a sphere's equation in spherical coordinates.

So, do you have any idea what "my" equation looks like on a graph?
 
  • #4
It's a quartic of some kind. Clear the square roots and fractions and I believe you will have a fourth degree equation.
 

1. What is the formula for converting spherical coordinates to rectangular coordinates?

The formula for converting spherical coordinates (r, θ, φ) to rectangular coordinates (x, y, z) is:
x = r * sin(θ) * cos(φ)
y = r * sin(θ) * sin(φ)
z = r * cos(θ)

2. How do you determine the values of r, θ, and φ for a given point in spherical coordinates?

The values of r, θ, and φ can be determined by using the distance formula and trigonometric functions.
r = √(x² + y² + z²)
θ = arctan(y / x)
φ = arccos(z / r)

3. Can spherical coordinates be negative?

Yes, spherical coordinates can be negative. The r value can be negative if the point is located in the opposite direction from the origin, while the θ and φ values can be negative if the point is in a different quadrant or hemisphere.

4. What is the difference between spherical and rectangular coordinates?

The main difference between spherical and rectangular coordinates is the way they represent a point in 3D space. Spherical coordinates use a distance from the origin (r), an angle from the positive z-axis (θ), and an angle from the positive x-axis (φ), while rectangular coordinates use the Cartesian coordinates (x, y, z) which represent a point's distance from the x, y, and z axes.

5. Can you convert rectangular coordinates to spherical coordinates?

Yes, rectangular coordinates can be converted to spherical coordinates using the following formulas:
r = √(x² + y² + z²)
θ = arctan(y / x)
φ = arccos(z / r)

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