love it but seen it before... sorry

can someone tell me where the mistake is? i'm curious!

One i can't solve. Darn!!!!!!!!!!!

The problem is that the large diagonal in the 5x13 is not really a straight line. You can't really line up the hypotenuse of the 3x8 right triangles with that of the 2x5 right triangles involved in the creation of the quadrangles.

I think I see the "mistake" but I'm not sure how to explain...

the solution is in the angles

Complementing Bob's comment, the shapes of the 8x3 triangles of the two rectangles are not identical. The hypotenuses of that "triangles", in the second rectangle, was forcelly distorced. In fact, these shapes are not triangles.

No~~ Google ruined the illusion. If you make the picture smaller (which google did), you can see where the problem is. (It's the abnormality.)

Bob's right. On the rectangle the hypotenuses don't make a straight line. What's more, the right angled triangle doesn't fit Pythagoras' theorem.

http://i201.photobucket.com/albums/aa2/franz9265/geometry.jpg

The image explains what's wrong in the illusion.

Wow, that is good! I had to work it out mathematically before i saw what was going on. Once i realised that the shapes could not possibly fit together properly in the second arrangement i saw that the angles were indeed slightly distorted.

The true area is 64 squares.

the hypotenuses on the 5x13 are not a straight line. the extra area makes up the 1 square unit difference

Bob and Paulo are correct. If you assume the shapes have been drawn correctly and do the math, the 5 x 13 one actually works out to 64, not 65. The lines between the triangles and the trapezoids have been distorted.

Triangles: 1/2 x base x height = 1/2 x 3 x 8 = 12 each

Trapezoids: 1/2 x (a + b) x height = 1/2 x (3 + 5) x 5 = 20 each.

12 x 2 + 20 x 2 = 24 + 40 = 64

paulo segio helped me to spot it but i'm still not sure how it makes that much of a difference. i see though that one of the triangles isnt actually a triangle.

interesting one.

This is the way it is because it is.


I don't get it.

Its not the overall size that is important - its the area of each shape. There are 2 shapes that have 24 squares, and 2 shapes with 20 squares. 24+24+20+20= 88 squares in both layouts

i could prolly expane this on the spot right now, but nun o yal would listen.

For the pieces to fit perfectly, the slopes of the shapes have to be exact. Calculating the slope of the quadrangle we get 5/2 or 2.5. The slope of the triangle is 7/3 or 2.333. If you used actual pieces put together, there sould be a slight gap which would account for the exta unit of area.

Reducing the size or quality of the illusion doesn't change the fact that it's geometrically impossible to fit those shapes together to form the perfect right angles in the 5x13 rectangle. Any freshman math student could sit down and mathematically prove that shape is impossible with true triangles.

It's the way it's arranged.. the numbers give it away

Yeah, like someone has said before, the hypotenuses of the two triangles do not line up with each other. If you do a bunch of calculation, you'll get the total angle (from those two angles involving in the 2 triangles) to be 190.something degree => that's the mistake.

If you compare the triangles in the smaller figure with the triangles in the larger figure, you will see that they are not the same and the larger figure actually contains distorted triangles. I can see this from a glance but if you want to prove it, simply count off the rectangle inside the triange formed by 2x3 squares or 6 squares. This rectangle fits inside the triangles in the larger figure but does not fit inside the triangles in the smaller figure. Thus the distorted triangles have each been enlarged enough to fill up an extra .5 of a square. .5 x 2 = 1 which accounts for the extra 1 unit squared.
I like this one.

the line in the middle of 8x13 isnt straight!

There is a lot of talk about distorted this and abnormal that, but I'd like to attempt more of a "math" answer as to why this is impossible.

Assume that each right triangle has a base of 8 and a height of 3 (as in the 8x8 image). This means that the slope on the triangle is 3/8. Or simply that for every 3 the slop moves in either an X or Y direction, that it must also move by 8 in the Y or X direction.

Then consider that the trapezoid has sides 5, 5, and 3. This means the trapezoid has a slope of 2/5.

For the two slops to line up, and all right angles to remain square with the X,Y grid, then the slope of the triangle (3/8) would have to equal the slope of the trapezoid (2/5). And since 3/8 = 15/40 and 2/5 = 16/40, then clearly 16 does not equal 15 so the slopes cannot be equal, and thus we have a (weak) proof that the given rearrangement of the shapes is not possible.

Hence, we have an illusion, which is what this is site is all about anyway. Thanks for the cool mental exercise.

the first geometry illusion that was posted on this site was given to us on a brain teaser page in my AP Physics class. it asked how it was possible.

i said because it wants to.

it makes sense now that its been explained, but its still rather hard to believe.

the triangles in the second box r not triangles. they r slightly curved outward and inward slightly. if the xtra spaces r added up, they equal 1 square.

In the 5x13 image, the 2 shaded shapes (that appear to be right angled triangles until closely examined) are actually quadrilaterals (four sided shapes), the line that appears to be the hypotenuse is actually 2 lines, one being at a slightly different angle.

they are both not rectangles. one is a square and the other is a true rectangle. squares have a larger surface area in general. so the mistake is in thinking they are both rectangles in my perspective.

bob is right. if you look at the line connecting the triangles in the 65 one, the line bends slightly. try putting a ruler or a flat edge up to the line, you can see that it curves.

Hey piece of cake...

They aren't triangles in the second rectangle (5x13)they are quads.

the line that runs across the one that adds up to 65 is not strait and if the gaps that would be there if it was strait add up to 1

I don't think the previous explainations are clear, so I will rephrase.

As you can see in the first diagram, the gray shape angles are 2x5. The yellow shape have an angle of 3x8.

These two angles are not the same and the won't fit each other. In the second picture it shows the two angles together. In reality it wont work, in the second picture there will be a sliver of space between gray and orange shapes. That sliver is equal to the extra space.

Um... I can see where the problem is, but it's kind of hard to explain...
The shapes of the different shapes (and yes, I do realize that is kind of awkward wording)INSIDE of the bigger shapes are distorted. Anyways, FYI, paulo sergio, distorced is not a word.

To calculate the angle, use arctan 8/3 = 69,4 degrees,
While arctan 5/2 = 68,2 degrees.
So the angles are not the same.
You can even see the the line is not a straight line.

Picture 64 is ok.

Picture 65 has a mistake:
The top line of the left tirangle is 3 units,
and the remaining left seems to be 2.
But the left triangle at this position ist only 1,875.
So there is a (square) gap between the triangles (and a triangle gap between grey and orange).

You can't see the gap in this picture, but you can calculate it. It's exactly 1 unit².

I think Bob is right!
the 2 rectangles 5x13 and 8x8 don't contain the same shapes, but in the 5x13 rectangle there are 2 quadrangles that are very similar to the 2 trinagles in the 8x8 rectangle. So we can't compare different shapes and try to find the same area.

I did make one of myself.
If you make first the one on the left en move the 4 objects like the one on the right i get a big gap betwen the diagaonal line.

Yea if you look closely at the 65 one the line that the two 'tiangles' make is wobbly. Also this illusion is similar to another one i saw on this site which explains in detail what is going on

BAH, Too boring for the morning. I need something more.

The problem on the 65 one is where the two orange triangles are touching, if you look hard enough you can see a kink when they meet, the diagonal goes through 1x3 squares whereas when its an orange and grey shape next to each other the diagonal only goes through 1x2.5 squares.

The shapes in the first 8 by 8 picture do not actually fit together in the way depicted in the 13 by 5 one. The slope of the diagonal side of each of the triangles (yellow) is 8 over 3. 8/3=2 2/3 or 2.6666667. The slope of each of the diagonal sides of the quadrilaterals (gray) is 5 over 2. 5/2=2 1/2 or 2.5. 2.5 does not equal 2.6666667, therefore the shapes cannot be put together contiguously in a way to create a 13 by 5 shape. The reason for the larger area is precisely this disparity of angle, as there should actually be a sliver of empty space from the bottom left to the top right.

In the second figure. If you add the angles of the up right are 88.4546º It is not a right angle, then the main diagonal is not straiht

Bob and Paulo Sergio are right on the ball. Using a straight edge you can see the bend in the hypotenuse of the shapes thus it is no longer a triangle

I still don't see it. Please explain!

I remember this one from geometry. Bob is close and it is in the angles. The easiest way to see how this works is by getting graph paper and cutting the shapes out. Then put them together in the second configuration. What happens is the angle of the diagonals between the triangle and the quadrelateral don't line up perfectly because they are not the same. This leaves a thin quadrelateral gap along the diagonal of the 5x13 diagram. The area of this gap is exactly the same as the area of one block and that is what accounts for the increase in area. With line thickness in this drawing they can cover up the gap but if you actually make the figures it's obviously there.

second design is wrong. The long trasversal line is not a line but is a fragmented line.
Little errors make the square.
Bye

Dave

Nice one

The posed question was, "if the shapes are the same size and area," but they are not. IN particular the orange triangles in the 64 sq configuration are right triangles with sides 3x8 note the "pitch" or slope is 8 horizontal squares per 3 vertical... or 2 2/3 horizontal for each vertical. In the second picture we can clearly see the pitch change from 3 to 1 in the region where the orange "triangles" touch (the width changes from 3 to 2 in the change of elevation of three) to 5 to 2 or 2.5 to 1 for the remainder of the polygon. This indicates that these are not really triangles but quadralaterals. Since they are not triangles at all, they cannot be the same triangles as in the other picture.

The flaw is in the poor picture quality with border lines too thick to see. If you were to cut shapes in a paper sheet and align them accordingly you would see that in the 5X13 shape there would be a gap area with no paper.
This is the missing area (65-64). But, the gap is so thin that you cant see it in the picture. A simple math test is to divide 5/2 and 8/3. They would be equal in the absence of gap. In this case we get 2 1/2 and 2 2/3 respectively. Because of the different angle you get this area gap. Amusing !

indeed the two figures contain the same 4 components but arrange differently with the 8x8 packed in most optimal way.

furthermore, the difference between the 8x8 cube and the 5x13 rectangular is that the later contains 2 shared angle points each 0.5 (at H5-6:W2-3 and H8-9:W3-4). the addition of those 2 points create the additional square (1x1) and therefore 64+1=65

This one is a bit weak. It is obvious to the eye that both triangles on the right do not build a straight line. In fact, those are not triangles, they are "quadrangles".

Hey, Black Mamba, thank you very much. I have a poor English and I was very tired to look for a dictionary. ;)

I think there is hole in the middle - very long and very narrow.