Answer to illusion #20: How Can This Be True

How can this be true???? Have a look at the picture (click to enlarge.) All the lines are straight, the shapes that make up the top picture are the same as the ones in the bottom picture so where does the gap come from????

This puzzle is something of an optical illusion, but it does have a solveable answer so i thought i would include it.

Before reading the answer can I interest you in a clue?

If you can't see the solution by looking you could try printing it and with your eye close to the page looking along the diagonals.

Failing that then let me just tell you the answer....

The green triangle has dimensions 2 x 5 and gradient 2 / 5 = 0.4

The red triangle has dimensions 3 x 8 and gradient 3 / 8 = 0.375

Hence the gradient of the green triangle is greater than that of the red triangle.

An exaggerated outline might look like....

In summary the missing square in the bottom triangle is made up for by the fact that it's hypotenuse bends out where as for the top triangle it bends in.

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