Сократим <span>3x и x^2, получим </span>х=-1
19.56*17.39-7.39*19.56=19.56(17.39-7.39)=19.56*10=195.6
Ответ: - 27/23 или - 1 4/23
Sia*sinb=1/2(cos(a-b)-cos(a+b)
sinx/2sin3x/2=1/2(cos(-x)-cos2x)=1/2
cosx-cos2x=1
cosx-2cos²x+1=0
cosx=a
2a²-a-1=0
D=1+8=9
a1=(1-3)/4=-1/2⇒cosx=-1/2⇒x=+-2π/3+2πn,n∈z
a2=(1+3)/4=1⇒cosx=1⇒x=2πk,k∈z
4-4х+х^2-х^2-3х=18
-7х=18-4
-7х=14
х=-2