Arrrrgghhh My Eyes

Logic Level 4

How many triangles are in this picture?


The answer is 260.

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2 solutions

Jos Dan
Jul 7, 2015

For a m × n m \times n rectangle, where m > n m>n , there are:

2 [ ( m + 1 2 ) + n ] + 2 [ ( n + 1 2 ) + n ] 2[ {m+1 \choose 2} + n] + 2[ {n+1 \choose 2} +n] triangles.

There are two types of triangles in this picture. Right-angled (green) and isosceles (blue).

Number of green triangles formed on every side is n n .

Number of blue triangles formed on side m is ( m + 1 2 ) {m+1 \choose 2} . This because you can choose two red dots to be the base of your triangle out of ( m + 1 ) (m + 1) dots.

For a square (m=n), formula becomes:

2 m [ m + 3 ] 2m[m+3]

In this case m = 10 m=10 , so the answer is 260 \boxed{260} triangles.

Wooooo, you should post a separate question for that :)

Pi Han Goh - 5 years, 11 months ago

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will do :)

Jos Dan - 5 years, 11 months ago

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link

Jos Dan - 5 years, 11 months ago
Rohit Ner
Jul 5, 2015

We get 40 40 right angle triangles as depicted above. And we get 40 40 triangles having a side of 1 1 segment, 36 36 triangles having a side of 2 2 segments, 32 32 triangles having o side of 3 3 segments and so on up to 4 4 triangles having sides as 10 segments. No further counting is possible. Thus the total no. of triangles is = 40 + 40 + 36 + 32 + . . . + 4 = 40 + 4 ( 10 + 9 + 8 + . . . + 1 ) = 40 + 220 = 260 =40+40+36+32+. . .+4\\ =40+4(10+9+8+. . .+1) \\=40+220 \\ \Huge\color{#3D99F6}{=\boxed{260}}

If you start counting triangles you will find 20 triangles in length and 20 triangles in the height therefore it should be 40 because rest of the image are just parallelograms

Syed Baqir - 5 years, 11 months ago

How did you make this Gif?

Pi Han Goh - 5 years, 11 months ago

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Did this on my phone, arghh my eyes indeed.... @Rohit Ner cool gif👍👍

Beakal Tiliksew - 5 years, 11 months ago

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Thank you :)

Rohit Ner - 5 years, 11 months ago

It took me 15 minutes to make it. I wanted to make a nicer one but lost my patience. :P and posted this incomplete gif.

Rohit Ner - 5 years, 11 months ago

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No, I mean, what is the process of making this gif? Is there an App for it? Did you use magic? Is there a pre-existing image you have on your computer? Did you use telekinesis?

Pi Han Goh - 5 years, 11 months ago

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@Pi Han Goh Actually I edited each and every image and just compiled it into an online gif maker.
PS : I wish god gave me the power to use telekinesis.

Rohit Ner - 5 years, 11 months ago

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@Rohit Ner Oh cool, do you have a link for the online gif maker?

Pi Han Goh - 5 years, 11 months ago

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@Pi Han Goh There are plenty like this one .

Rohit Ner - 5 years, 11 months ago

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@Rohit Ner Ohhhh I'm always curious to learn it but I couldn't find a site that's super easy to use. I'll give it a try.

Thank you.

By the way, the generalization of the n × n n \times n grids is 2 n ( n + 3 ) 2n(n+3) . In this case, it's n = 10 n=10 .

Pi Han Goh - 5 years, 11 months ago

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@Pi Han Goh What about m × n m\times n

Kyle Finch - 5 years, 11 months ago

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@Kyle Finch IDK, I haven't experimented on that yet. Maybe you should post a question about it. ;)

Pi Han Goh - 5 years, 11 months ago

@Rohit Ner I do not understand how to to use it , please show it.

Raven Herd - 5 years, 11 months ago

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@Raven Herd Just upload the images in a sequential order as you want them in the gif.

Rohit Ner - 5 years, 11 months ago

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