Cartesian Isometric

The graph below is an oblique coordinate system based on 60 degree angles. It was drawn on isometric paper. What kinds of triangles do these points form?
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Problem



The graph below is a coordinate system based on $60$ $^\circ$ angles. It was drawn on isometric paper.
Image
Cartesian Isometric


The marked points are $(6, 2)$, $(6, 5)$ and $(9, 2)$. When joined they form an equilateral triangle.

The following five sets of points are also triangles.

A. $(1, 13), (6, 8)$ and $(6, 13)$.

B. $(1, 1), (3, 3)$ and $(7, 1)$.

C. $(12, 1), (17, 1)$ and $(8, 9)$.

D. $(1, 10), (5, 2)$ and $(6, 6)$.

E. $(7, 5), (15, 4)$ and $(7, 11)$.

What kinds of triangles are they?

Can you work out any of the angles at the vertices?