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I wanted to plot a 3-D solid region, in which my function f(x,y,z)=

x (1/(1 + 0.06))^3 + y (1/(1 + 0.06))^2 + (2 z^2)/15  (Sin[10 Degree])^2 -z/3  Cos[10 Degree]

is non-positive,where x, y and z are 3 variables. As can be seen in the following fig. enter image description here

I think I should first find out the neutral surface, on which f(x,y,z)=0, it is denoted as the red surface in the fig. I have tried Plot3D and ParametricPlot3D:

Plot3D[x (1/(1 + 0.06))^3 + y (1/(1 + 0.06))^2 + (2 z^2)/15  (Sin[10Degree])^2 - z/3  Cos[10 Degree], {x, 0, 8}, {y, 0, 8}, {z, 0, 82}]

and

ParametricPlot3D[x (1/(1 + 0.06))^3 + y (1/(1 + 0.06))^2 + (2 z^2)/15  (Sin[10 Degree])^2 - z/3  Cos[10 Degree], {x, 0, 8}, {y, 0, 8}, {z, 0, 82}]

But MMA reports nonopt: Options expected (instead of {z,0,82}) beyond position 3

I do know the plot of 2 variables define the 3D surface. And the plot of 3 variables define 3D space in 4D space. So, how can I to visualize the plot of 3 variables. Is there some way to use ParametricPlot3D, Plot3D or any other Mathematica functions to perform this task?

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  • $\begingroup$ Can anyone get me a code for this example: Draw a tangent plane and a normal for the area z=x^2/2-y^2 at the point M(2,3,5)? $\endgroup$
    – Biljana
    Commented May 3, 2017 at 22:06

2 Answers 2

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sf[x_, y_, z_] :=  x (1/(1 + 0.06))^3 +  y (1/(1 + 0.06))^2 + 
                (2 z^2)/15 (Sin[10 Degree])^2 - z/3 Cos[10 Degree];

ContourPlot3D[sf[x, y, z] == 0, {x, 0, 8}, {y, 0, 8}, {z, 0, 82}]

enter image description here

sz[x_, y_] := z /. Solve[sf[x, y, z] == 0., {z}];

Plot3D[Evaluate@Quiet@sz[x, y], {x, 0, 8}, {y, 0, 8}, BoundaryStyle -> None,
       Mesh -> None, BoxRatios -> 1]

enter image description here

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To plot a "solid region" as you request, you can use RegionPlot3D

f[x_, y_, z_] := 
 x (1/(1 + 0.06))^3 + 
  y (1/(1 + 0.06))^2 + (2 z^2)/15 (Sin[10 Degree])^2 - 
  z/3 Cos[10 Degree]

RegionPlot3D[
 f[x, y, z] < 0, {x, -2000, 2000}, {y, -2000, 2000}, {z, -2000, 2000}]

enter image description here

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  • $\begingroup$ Thanks, @kguler! I have learned the ContourPlot3D from you. $\endgroup$
    – Enter
    Commented Nov 2, 2014 at 13:04
  • $\begingroup$ Thank you,@rhermans! I have learned the use of RegionPlot3D from your answer! Although I have accepted the reply offered by @kguler, I do think your answer is very useful as well! But stack only allows to accept one answer, sorry about that! $\endgroup$
    – Enter
    Commented Nov 2, 2014 at 13:06

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