### 11.8.4 Equilateral triangles in the plane: equilateral_triangle

See section 12.7.4 for equilateral triangles in space.

The equilateral_triangle command takes two arguments and an optional third. The two mandatory arguments are points A and B.

equilateral_triangle returns and draws the equilateral triangle ABC, where AB to AC is counterclockwise.
Input:

equilateral_triangle(0,2)

Output:

The optional argument needs to be a variable name which is assigned to vertex C.
Input:

equilateral_triangle(0, 2, C)

Output:

Input:

affix(C)

Output:

i*sqrt(3) + 1