Two waves y1=A1sin(ωt−β1), y2=A2sin(ωt−β2)Superimpose to form a resultant wave whose amplitude is
A12+A22+2A1A2cos(β1−β2)
A12+A22+2A1A2sin(β1−β2)
A1+A2
|A1+A2|
Phase difference between the two waves is φ=(ωt−β2)=(ωt−β1)=(β1−β2)∴Resultant amplitude A=A12+A22+2A1A2cos(β1−β2)