Puzzle | Guess the shape

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