An equilateral triangle stacked on a pentagon. What’s the angle?
Scroll down for a solution to this problem.
Solution
The angle is 48°.
![](https://mirangu.com/wp-content/uploads/2021/01/SpinningTopSolution.jpg)
First we recognise the isosceles triangle EDF. It has a top angle of 108°+60°=168°. From the interior angle sum we deduce that the two other angles must be 6°.
From reflection symmetry in the line through F it is seen that α + 2*6°=60°. Hence α = 48°.
Visual solution
![](https://mirangu.com/wp-content/uploads/2021/01/SpinningTopDavid.jpg)