Since the reflected wave and the incident wave add to each other while moving in opposite directions, the appearance of propagation is lost and the resulting vibration is called a standing wave. When sound waves in air (pressure waves) encounter a hard surface, there is no phase change upon reflection. That is, when the high pressure part of a sound wave hits the wall, it will be reflected as a high pressure, not a reversed phase which would be a low pressure.
A principal diagonal of a hexagon is a diagonal which divides the hexagon into quadrilaterals. In any convex equilateral hexagon (one with all sides equal) with common side a, there exists a principal diagonal d 1 such that.
We can then draw a right triangle using the vertex-to-vertex diameter of the hexagon as a hypotenuse. Since the diameter of such a hexagon is known to be 2, we are left with one undefined edge of our triangle, equal the distance between two opposing edges of the hexagon (which is twice the apothem).