Carcass wrote:
There are 12 points at EQUAL interval..
So the isosceles triangle can have EQUAL sides of length.
Let's work on the central vertex.
A as the vertex between EQUAL sides..
The EQUAL sides can be 1 unit, two unit, 3 unit, 4 unit or 5 unit...
6 unit will be the diameter so not possible.
So A as central vertex can make 5 isosceles triangles.
Thus 12 vertices from A to L can make 12*5=60 such isosceles triangles.
However 4 units results in an equilateral triangle.
So we are counting the same triangle THREE times.
So actual different triangles with 4 unit as length = 12/3=4..
So we have 12-4=8 extra triangles counted..
Total = 60-8=52...
B
I might be missing something but how does when know that a unit 4 will create a equilateral triangle