he points of this 3-by-3 grid are equally spaced horizontally and vertically. How many different sets of three points of this grid can be the three vertices of a triangle?
+2264
[T]he points of this 3-by-3 grid are equally spaced horizontally and vertically. How many different sets of three points of this grid can be the three vertices of a triangle?
9C3 = 84
minus 8
answer 72
I based this answer on the reasoning that a
triangle can be drawn using any three points
in the grid, except when those three points lie
in a straight line.
.
