1. Nine points are arranged in a 3 x 3 grid, as shown below. In how many different ways can you choose three points, so that they form a triangle?
2. A right isosceles triangle has a hypotenuse of 1. What is the area of the triangle?
1. There are 44 ways of forming triangle.
There are 9C3 = 84 ways to choose 3 dots.
There are 8 ways that those 3 dots can all be in a row.
I think that there are 84-8 = 76 different triangles that can be formed.