Refer to the attached image in the step-by-step part below.
Work Step by Step
Every next figure adds 1 triangle (and/or one diagonal from the same vertex) and 1 side to every shape.
You can help us out by revising, improving and updating this answer.Update this answer
After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.