Missing square puzzle animation. When the quadrilaterals are rotated about their centers they fill the space of the small square, although the total area of the figure seems unchanged. The apparent paradox is explained by the fact that the side of the new large square is a little smaller than the original one. A more complete explanation can be found in <a href="https://en.wikipedia.org/wiki/Missing_square_puzzle" class="extiw" title="en:Missing square puzzle">Missing square puzzle</a>.
<a href="//commons.wikimedia.org/wiki/User:Alvesgaspar" title="User:Alvesgaspar">Joaquim Alves Gaspar</a>
CC BY 2.5
<span class="int-own-work" lang="en">Own work</span>