The sum of the shorter two lengths is exactly equal to the longer length. The "triangle" made by these segments will look like a line segment of length 12. It will have zero area.
Many authors would tell you this is <em>not a triangle</em>. (Others will tell you it is a triangle—a degenerate case.)
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These numbers are an arithmetic sequence. The ratio of lengths is 1 : 2 : 3. The only arithmetic sequence of side lengths that makes a right triangle are those in the ratio 3 : 4 : 5.
