Sierpinski's Triangle - 1

Geometry Level 3

Sierpinski's Triangle is a self-similar fractal. To construct it do the following:

Take a red equilateral triangle of area 1. For each red triangle:

  • Find the midpoint of all sides.

  • Connect the midpoints.

  • Shade the formed triangle white.

If you repeat these steps (in the bullet point list) an infinite amount of times, the limit will be Sierpinski's triangle.

Let step 0 be the step for which the triangle is completely red.

Colors are chosen at random.

Question: In step n n of Sierpinski's triangle, there are x x red triangles, how many red triangles will there be in step n + 1 n+1 ?

See the next problem .

Note: This problem is part of a set of problems, further investigating Sierpinski's Triangle in different ways. If you want to continue investigating click here . Questions will increase in difficulty.

Image Credits: Sierpinski's Triangle Image created by William Andrus. Removed grey outline.

x + 3 x + 3 4 x 4x 3 x 3x None of these. 2 x 2x

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1 solution

Mihael Keehi
Mar 13, 2018

At step 0 we have only 1 1 red triangle

At step 1 the previous red triangle is divided into four identical triangles, 3 3 of which are red . Hence, there are 3 ( 1 ) = 3 3(1)=3 red triangles .

At step 2 each red triangle in the previous step is divided into four identical triangles, 3 3 of which are red. Therefore, since there were 3 3 red triangles in step 1 , now there will be 3 ( 3 ) = 9 3(3)=9 red triangles .

At step 3 each red triangle in the previous step is divided into four identical triangles, 3 3 of which are red. Therefore, since there were 9 9 red triangles in step 2 , now there will be 3 ( 9 ) = 27 3(9)=27 red triangles .

Repeating this process, we get that if at step n n there x x red triangles then at step n + 1 n+1 we will have 3 x 3x of them.

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