Sin4x-sin(π/2-6x)=2*sin(4x-(π/2-6x))/2
*cos(4x+π/2-6x)/2=
2*sin(4x-π/2+6x)/2*cos((π/2-2x)/2=
2*sin(10x/2-π/2:2)*cos(π/2:2-2x:2)=
2*sin(5x-π/4)*cos(π/4-x)
Cos²x +sin2x - 2cosx - 4sinx =0 ;
cos²x +2sinxcosx - 2cosx - 4sinx =0 ;
cosx(cosx +2sinx) -2(cosx +2sinx) =0 ;
(cosx +2sinx)(cosx -2) =0 ; [ cosx ≠ 2 ].
cosx+2sinx =0;
ctqx = -2;
x = - arcctq2 + π*n , n ∈ Z.
D= -8²-4*1*(-20)=64+80=144
x1=8+√144/2=8+12/2=20/2=10
x2=8-12/2=-4/2=-2