What Is Going On Here?

Here is a confusing mathematical paradox involving the chessboard.   Cut the board with three straight cuts (left). Then rearrange the pieces into a rectangle (right).

 

 

 

 

 

 

 

The area on the left is 8x8=64, but the area on the right is 5x13=65. Where did the extra square come from?!  Prof. Christian Hesse explains HERE