# Math Help - plot3d mathematica 7

1. ## plot3d mathematica 7

hi,
i have two quistions
1. how to draw graph by using Plot3D for "x^2+y^2=z^2"
2. in Plot3d how to change the Symmetry axis in the graph, in x^2+y^2=z^2 by changing the Symmetry axis to y.

2. Originally Posted by acied
hi,
i have two quistions
1. how to draw graph by using Plot3D for "x^2+y^2=z^2"
2. in Plot3d how to change the Symmetry axis in the graph, in x^2+y^2=z^2 by changing the Symmetry axis to y.
1.

My experience has been that it's hard to plot non-functions in Mathematica. So my approach would be:

Code:
Line 1: f[x_, y_] := Sqrt[x^2 + y^2]
Line 2: Plot3D[{f[x, y], -f[x, y]}, {x, -10, 10}, {y, -10, 10}]
2.

I don't know what you mean by this.

3. ## Clarification for 2

in the x^2+y^2=z^2 the Symmetry axis is Z axis, and i have to change it to another Coordinate axis, like y or x

4. Originally Posted by acied

in the x^2+y^2=z^2 the Symmetry axis is Z axis, and i have to change it to another Coordinate axis, like y or x
I guess you mean plane of symmetry is z = 0, and you want to change it to y = 0.

First of all, x^2+y^2=z^2 is already symmetric about the plane y = 0.

Second, if you want to rotate the graph, couldn't you just write x^2 + z^2 = y^2?

5. thanks i will try your Suggestion, but it will not rotate, its shows the same graph

6. Originally Posted by acied
thanks i will try your Suggestion
Sorry, I just realized there is a special rotational symmetry about the z-axis, and no need to interpret with planes. If you want to change this to the y-axis then x^2+z^2=y^2 should be it.

7. its shows the same graph without rotating

8. Originally Posted by acied
its shows the same graph without rotating
You probably didn't type it in properly. You have to solve for z.

Code:
Line 1: f[x_, y_] := Sqrt[y^2 - x^2]
Line 2: Plot3D[{f[x, y], -f[x, y]}, {x, -10, 10}, {y, -10, 10}]

9. thankssssssssssssssssssssss