Can someone explain #20 here?

[closeupready]

http://diply.com/trendyjoe/29-optical-illusions-that-will-seriously-mess-with-your-mind/43597/5

I've tried to understand how this can happen - oh wait, I just thought of something, did they cut out the box in moving it???

[arcane1]

1. I think the base of the red triangle is longer than the green and yellow shapes.

Cool site!!! Thanks for posting. Now I'm off to check out the rest

[closeupready]

2. They're all pretty fun, but that was the only one that

got me thinking, 'how'd they do that?' lol

[arcane1]

3. I'm stumped on #1, the cars of different sizes.

I can't figure out why the closest one seems smallest

[GeorgeGist]

4. here you go ...

درس ریاضیات به منظور به کارگیری تجسم هندسی دانش‌آموزان مطرح می‌شود.
این پازل دو ترکیب از اشکالی را نشان می‌دهد که ظاهراً در مجموع، دو مثلث قائم‌الزاویهٔ هم‌نهشت هستند. اما یکی از آنها یک مربع ۱×۱ فضای خالی دارد. دلیل به وجود آمدن مربع خالی این است که برخلاف فرض بیننده، هیچ کدام از دو شکلِ به‌ظاهر مثلثِ به دست آمده، مثلث نیستند و در واقع چهارضلعی هستند و این دو چهارضلعی نیز با هم همنهشت نیستند و البته چشم طبیعی انسان قادر به این تفاوت نمی‌باشد. برای ارزیابی بیشتر این تصویر را ببینید.
بایگانی – مشاهدهٔ نگاره‌های برگزیدهٔ بیشتر...
نمایش - ویرایش

[closeupready]

5. Aha, so I was right!

Aren't I smart?

[closeupready]

6. Here's the wiki on this:

http://en.wikipedia.org/wiki/Missing_square_puzzle

Layman's terms: If you look closely at the two triangles, you can see that they are NOT simply two identical forms, one larger than the other - the bigger triangle has a slope of about 30 degrees, and the smaller one of 35 degrees - thus allowing space for the 'missing' square in the re-assembled structure.

[denbot]

7. Gauh!!!

Witchcraft! Witchcraft, I tells ya!

[begin_within]

8. I think I have it.

The second arrangement, with the extra white square, goes slightly higher up on the grid than the first arrangement. That makes up for the white square.

Keep your eye on the point on the grid where the green and red shapes meet (when the green is at the top). Then when the red slides up to the top, the red is a little higher than that point. So it's not even in the same place.

So the combined shapes are going up higher the background. You don't notice that, because the increase is spread out over a slope. But you do notice the white square.

Conversely, keep your eye on the point of the grid where the red and green meet, when the green is at the bottom. You will see that where the shapes meet moves down.

That's what makes up for the loss/gain of the white square.

The pieces never do form a perfect triangle, because the slope of the green is different from he slope of the red, and thus they do not form a hypotenuse. Close, but just enough off that you don't notice.