Admittedly, this is not in English. I know I’m tired, but I’m not that tired.

I’m decent at mathematics, and maybe it’s because I’m tired that this isn’t making sense to me. My question is, what kind of slight of hand is going on here?

Is there just something with the dimensions that I’m missing?

I tried pausing it and counting the boxes, to no avail, I couldn’t find the trickery.

The diagonal line in the new rectangle is not a straight line (it’s just close). Calculate the slope of each segment and you’ll see what I mean. The difference between the actual diagonal and a true line accounts for the missing square.

The slope of the quadrilateral (2/5) is not the same as the slope of the triangle (3/8). Therefore combining the two does not actually create a larger triangle as depicted.

They may be displaying a straight line and fudging the areas, or simply displaying a crooked line that the eye can’t detect. In the latter case I’d expect you might be able to see the crookedness if you shift the images so that the hypotenuse of the large ‘triangle’ runs vertically (people are better at noticing discrepancies in horizontal or vertical lines).

The embarrassing part of this for me is that… you guessed it, I’ve heard of the Missing Square Puzzle before. :smack:
Lets pretend that I never made this thread…

I would guess that is especially true on a computer screen where diagonal lines look (for lack of a better word) more pixely than horizontal or vertical ones.