Michael J. answered 08/30/17
Tutor
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(5)
Effective High School STEM Tutor & CUNY Math Peer Leader
The polygon has 3 vertices, so you will have a triangle. You need to find the lengths of each side formed by connecting the 3 points. You can find the lengths using the distance formula. Then add up the sides.
I recommend you plot these points on a coordinate grid for visualization.