See Section 27.6.4 for equilateral triangles in space.
The equilateral_triangle command creates equilateral triangles.
With the argument var, C will be assigned to var.
| equilateral_triangle(1/2+i/2,4+i) | 
 
| equilateral_triangle(1/2+i/2,4+i,C) | 
 
| evalc(affix(C)) | 
| 
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