Question

Cos(x+y) + cos(x-y) = 2cosx cosy​

Answer 1

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