WMC 2018 Senior Problem 20

Level 1

Start with an equilateral triangle of side 2 2 . Form a second equilateral triangle by connecting the midpoints of the first triangle. Form a third equilateral triangle by connecting the midpoints of the second triangle. If you continue this process indefinitely, what is the sum of the areas of all the triangles?

1 3 \frac { 1 }{ 3 } 4 3 3 \frac{4\sqrt3}{3} 5 3 3 \frac{5\sqrt3}{3} 7 3 3 \frac{7\sqrt3}{3} 8 3 3 \frac{8\sqrt3}{3}

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1 solution

X X
Oct 14, 2018

The area of an equilateral triangle of side 2 is equal to 3 \sqrt{3}

3 ( 1 + 1 4 + 1 16 + 1 64 + . . . ) = 3 × 4 3 \sqrt{3}(1+\frac14+\frac1{16}+\frac1{64}+...)=\sqrt{3}\times\frac43

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