What do we get when two sound waves of slightly different frequencies interfere with each other?
a. resonance
b. beats
c. standing waves
d. first harmonic

B. Beats

Explanation:

When two sound waves of slightly different frequencies are superimposed at a point in the space then the amplitude of resultant wave will change maximum to minimum cyclically with time.

This phenomenon of changing amplitude of sound with time is known as Beats.

So here we will have

now we have

so this above equation is for the BEATS

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.