Answer :
In order to prove that there are only four of these triangles, we need to first restate the formula for the perimeter of a triangle which is given as: P = a + b + c. Hence, we must identify all the triangles that have two or more equal sides, and each side is a whole number.
What is the proof?
Step 1 - First, we state all the possible combination three whole numbers which when added together result in fifteen.
The numbers are given as:
- 1 1 13
- 2 2 11
- 3 3 9
- 4 4 7
- 5 5 5
- 6 6 3
- 7 7 1
Step 2 - Eliminate options where a side is more than the sum of the other two sides
Hence,
- 1 1 13
- 2 2 11
- 3 3 9
are eliminated. The remaining triangles are four in number.
QED.
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