Помогите с 9 заданием

Question

Помогите с 9 заданием

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Answer 1

Sin(x)+sin(y) = 2·sin(½(x+y))·cos(½(x-y))
u=sinx+sin3x=2sin2xcosx
cos(x)+cos(y) = 2·cos(½(x+y))·cos(½(x-y))
v=cosx+cos3x=2cos2xcosx
cosx≠0  cos2x≠0;   u/v=sin2x/cos2x
sin2x=0   2x=πn  x=πn/2   n∈Z