1. Nodes and antinodes are known to form stationary waves. In a given stationary wave, the distance between any given two successive nodes is half the wavelength. The approximate distance between a node and the immediate next antinode is actually one-fourth of a given wavelength.

2,

That is, the circumference would be the length of the circle The area of a circle is pi (approximately 3.14) times the radius of the circle squared. ... If a circle has a diameter of 4, its circumference is 3.14*4=12.56. If you know the radius, the diameter is twice as large.