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?
+2381
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?
72
Let me tell you how I got that number.
I think that any combination of three dots in that 3x3 grid will form a triangle, except
the eight triples that lie in a straight line; namely, 3 vertical, 3 horizontal, 2 diagonal.
So I went 9C3 = 84 and then subtracted the eight straight lines that would be formed.
I posted this answer a while ago, but made a typo. I said 9x9 grid. Should been 3x3.
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