# What's wrong with geometry? [duplicate]

What's wrong with the puzzle in this video?

I didn't understand. Do you understand what happens?

(Click the image to open the video)

## marked as duplicate by Dan Russell, Engineer Toast, Gamow, Deusovi♦Aug 9 '16 at 21:00

Obviously, $64\neq65$. Observe the diagram below:
The slopes of the diagonals of the blue and pink pieces are each $2/5 = 0.4$, whereas the slopes of the diagonals of the green and red pieces are each $3/8 = 0.375$. Thus, while the shapes made by the top two and bottom two pieces may look like triangles, they are in fact concave quadrilaterals, which creates a thin white space between the pieces. This white space has area $1$, so the area, as expected, stays constant at $64$.