Equation for two waves is given as `y_(1)=asin(omegat+phi_(1)), y_(2)=asin(omegat+phi_(2))`.
If ampitude and time period of resultant wave does not change, then calculate `(phi_(1)-phi_(2))`.

Explanation

The equation of resultant wave is , `y=y_(1)+Y_(2)=asin(omegat+phi_(1))+asin(omegat+phi_(2))`
`=2asin(((omegat+phi_(1))+(omegat+phi_(2)))/(2))`
`cos(((omegat+phi_(1))-(omegat+phi_(2)))/(2))`
`=2acos((phi_(1)-phi_(2))/(2))sin[omegat+(phi_(1)+phi_(2))/(2)]`
The amplitude of the resultant wave is,
`A=2acos((phi_(1)-pphi_(2))/(2))` ltbgt Given, `A=a, ` then `a=2acos((phi_(1)-phi_(2))/(2))`
or `cos((phi_(1)-phi_(2))/(2))=(1)/(2)=cos60^(@)`
or `(phi_(1)-phi_(2))/(2)=60^(@) or phi_(1)-phi_(2)=120^(@)`