Can My Selfie Fit This Huge Frame?

Windows are back!

Here I connect some windows (see this to know what it is) to form an image frame.

The frame has thickness, width and height of 1 , 2016 , 1008 1, 2016, 1008 , respectively. Here's the model:

How many triangles are there in the frame?

Bonus: Generalise it for a frame of size x × y x \times y .


The answer is 120876.

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1 solution

  • Count the triangles of a 1 1 by 2016 2016 chain: 20.2016 10 = 40310 20.2016-10=40310

  • Count the triangles of a 1 1 by 1008 1008 chain: 20.1008 10 = 20150 20.1008-10=20150

  • Sum up and minus the triangles of 4 windows in coner (they were counted twice each) : 2.40310 + 2.20150 4.12 = 120872 2.40310+2.20150-4.12=120872

Wait! We didn't count these 4 4 triangles:

The answer is 120872 + 4 = 120876 120872+4=120876

P/s: Yes, you can. Take a selfie :)

I think the most popular mistake is to forget the 4 4 corners, 'cause in the figure, the dot dot dot hides these triangles.

Tran Quoc Dat - 5 years, 1 month ago

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though i got it correct but i request you to mention that dimensions 2016 *1008 belongs to the external rectangle not internal.

aryan goyat - 5 years ago

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