9 / ( XY ) - 4 = 3X
9 - 4XY = 3X^2Y
9 = 3X^2Y + 4XY
9 = Y * ( 3X^2 + 4X )
Y = 9 / ( 3X^2 + 4X )
Если что не понятно - пиши!
Cosx+2cos2x=1
cosx+2(cos²x-sin²x)=1
cosx+2cos²x-2(1-cos²x)=1
cosx+2cos²x-2+2cos²x=1
4cos²x+cosx²-3=0
cosx=m
4m²+m-3=0
D=1²-4*4*(-3)=1+48=49=7²
m=(-1+7)/2*4=6/8=3/4
m=(-1-7)/2*4=-8/8=-1
cosx=3/4 ⇒ x=+/-arccos(3/4)+2πn
cosx=-1 ⇒ x=π+2πn, n∈Z
Sinα-sin(α+π/3)=2sin[(α-α-π/3)/2]·cos[(α+α+π/3)/2]=
=2sin(-π/6)·cos(α+π/6)=-2sin(π/6)·cos(α+π/6)=-2·1/2·cos(α+π/6)=
=-cos(α+π/6)