What is the altitude of an equilateral triangle with side 4 cm?
Or alternatively what is the ratio of the sides in a 30-60-right triangle?
Last option: a right triangle has hypotenuse 4 and one side 2. What is the length of the other side?
Draw a figure!!!
A regular hexagon is made up of 6 equilateral triangles.
The apothem of the hexagon is the same as the altitude of one of those triangles.
The altitude of the equilateral triangle divides it into 2 congruent 30-60 right triangles.
The hypotenuse of one of those 30-60 right triangles is the side of the hexagon, i.e. 4.
The short side of one of those triangles is 1/2 of the side, i.e. 2.
The altitude is the long side of the right triangle and the theorem of Pythagoras tells you that the long
side is sqrt(42 - 22) = sqrt(12) = 2sqrt(3).
Also for future reference for you, in a 30-60 right triangle the ratio of the sides is 2:1:√3.