The altitude of an equilateral triangle is 9 meters, what is the side length?

The altitude of an equilateral triangle separates it into two 30-60-90 degree triangles, and they have the ratio 1:sqrt3:2 (shorter leg: longer leg: hypotenuse), so divide 9 by the square root of 3 to find half of the length of a side:

9/sqrt3=9sqrt3/3=3sqrt3

Multiply by 2 two find the length of a side, which is 6sqrt3.