What shape completes the last line?

1. Triangle, Pentagon, Square
2. Square, Hexagon, Hexagon, Square
3. Pentagon, Hexagon, Hexagon, Hexagon, Square, Triangle
4. Hexagon, Octagon, Octagon, Octagon, Octagon _________ ?

Answer: Square
Explanation:
The first shape’s sides squared shall give the sum of sides in remaining shapes.

 1)   triangle pentagon square
sides:    3        5       4
 --->     32 = 9 = 5 + 4
2)    square hexagon hexagon square
sides:    4      6       6       4
 --->     42 = 16 = 6 + 6 + 4
3)    pentagon hexagon hexagon hexagon square triangle
sides:     5        6       6      6       4      3
 --->      52 = 25 = 6 + 6 + 6 + 4 + 3
4)  hexagon octagon octagon octagon octagon square
 sides:     6        8       8       8       8      4
 --->     62 = 36 = 8 + 8 + 8 + 8 + 4

Reference:
https://www.brainbashers.com/showpuzzles.asp

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