Question

Question #63916

Answer 1

`LHS=(sin3x+sinx)/(cos3x+cosx)`

`=(2sin2xcosx)/(2cos2xcosx)`

`=tan2x=RHS`

Using formula

`sinC+sinD=2sin((C+D)/2)cos((C-D)/2)`
`cosC+cosD=2cos((C+D)/2)cos((C-D)/2)`