Can anyone tell me why the first two ContourPlot3D calls don't work, but the third one does?
In[119]:= Clear["Global`*"]
In[120]:= A = {{1, 0, 5}, {-2, 1, -6}, {0, 2, 8}};
b = {2, -1, 6};
In[122]:= Thread[A.{x1, x2, x3} == b]
Out[122]= {x1 + 5 x3 == 2, -2 x1 + x2 - 6 x3 == -1, 2 x2 + 8 x3 == 6}
In[123]:= ContourPlot3D[%, {x1, -10, 10}, {x2, -10, 10}, {x3, -10, 10}]
Out[123]= ContourPlot3D[%, {x1, -10, 10}, {x2, -10, 10}, {x3, -10, 10}]
In[124]:= ContourPlot3D[
Thread[A.{x1, x2, x3} == b], {x1, -10, 10}, {x2, -10, 10}, {x3, -10,
10}]
Out[124]= ContourPlot3D[
Thread[A.{x1, x2, x3} == b], {x1, -10, 10}, {x2, -10, 10}, {x3, -10,
10}]
In[125]:= ContourPlot3D[{x1 + 5 x3 == 2, -2 x1 + x2 - 6 x3 == -1,
2 x2 + 8 x3 == 6}, {x1, -10, 10}, {x2, -10, 10}, {x3, -10, 10}]
