Geometric
Solution
to
The
15o
Problem
Recall, that we will be working with
a square ABDE.
Now let's choose a point C
so that the triangle CDE is isosceles with angles 15o
at D and E.
We want to find out what type of triangle
ABC is.
To begin, choose a point F inside
the triangle such that triangle BFD is congruent to triangle DCE.
Notice that BF is perpendicular
to CD of the equilateral triangle CDF.
By the previous statement, BC = BD
= AB.
Therefore, we can conclude that triangle
ABC
is equilateral.
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