Answer:
Step-by-step explanation:
the given equation
cos(x+y)+cos(x-y)=2cos(x)*cos(y)
[cos(x)cos(y)-sin(x)sin(y)]+cos(x-y)=2cos(x)*cos(y) ..
[cos(x)cos(y)-sin(x)sin(y)]+[cos(x)cos(y)+sin(x)sin(y)]=2cos(x)*cos(y)
[cos(x)cos(y)+cos(x)cos(y)]]+[sin(x)sin(y)-sin(x)sin(y)]=2cos(x)*cos(y) ..
2cos(x)*cos(y)=2cos(x)*cos(y)
L.H.S=R.H.S
Hence proved
