What type of interference results in beats?
constructive
destructive
negligible
interference is not involved in the creation of beats

constructive

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

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.