Answer: constructive
Step-by-step explanation:
Two waves having slightly different frequencies when interfere constructively produce beats. Superposition of these two waves results in addition of amplitudes of the two waves. The amplitude of the resultant wave vibrates or beats.
Beat frequency is given by the absolute difference between the frequencies of the two waves.
b = |f₂ - f₁| = f₂ - f₁ or f₂ + f₁