Пусть А:В=9:11. (2/3A) : В+1/3A= (2/3*9):(11+1/3*9)=6:14
-3х+4= -10-35-5х
-3х+5х= -49
2х=-49
х= - 24.5
Cos2a+2(sina*cos(п/6)+cosa*sin(п/6)*(sina*cos(п/6)-cosa*sin(п/6))=cos2a+2(sin^2(a)*cos^2(п/6)-cos^2(a)*sin^2(п/6))=cos2a+2(0.75*sin^2(a)-0.25*cos^2(a))=cos^2(a)-sin^2(a)+1.5*sin^2(a)-0.5*cos^2(a)=0.5(sin^2(a)+cos^2(a))=0.5