by Serhiy Grabarchuk Jr
This Christmas Tree contains three equilateral triangles.
By moving 3 matchsticks it is possible to get four equilateral triangles on the plain. No overlapping of the matchsticks is allowed.
In the illustration some matchsticks are adjacent to the respective Christmas decorations. It is known some of the matchsticks are never moved for the solution. To what decoration the unmoved matchsticks are adjacent?
The solution is based on the idea of moving either top or bottom triangle to the position shown in the illustration (or symmetrical one).
In either solution the middle triangle is never moved. Thus, neither of the two matchsticks adjacent to the middle decoration.