Since sinusoidal waves are cyclical, a particular phase difference between two waves is identical to that phase difference plus a cycle. For example, if two waves have a phase difference of $\backslash$pi $4\backslash$pi $4,$ the interference effects would be the same as if the two waves had a phase difference of $\backslash$pi $4+2\backslash$pi $\backslash$pi $4+2\backslash$pi $.$ The complete criterion for constructive interference between two waves is therefore written as follows:

phase difference$=0+2\backslash$pi nfor any integer nphase difference$=0+2\backslash$pi nfor any integer n

Write the full criterion for destructive interference between two waves.