A tessallation is an arrangement of repeating shapes that have what characteristics

A tessellation is an arrangement of shapes closely fitted together, especially of polygons in a repeated pattern without any gaps or overlapping.

Explanation:

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the answer would be the third option, "no, ariel should have added 9^2 and 12^2 and compared that to 15^2."

this is found through the pythagorean theorem, which is a^2 + b^2 = c^2.

this is the correct way of solving the problem:

9^2 + 12^2 = 15^2

81 + 144 = 225

225 = 225