1) -4a(a² - 3ab + 7b) = -4a³ + 12a²b - 28ab
2) -2c³d⁴(8c² - c³d + 4d³) = -16c⁵d⁴ + 2c⁶d⁵ - 8c³d⁷
S3=b1*(q³-1)/(q-1)=b1*(q²+q+1)=54*(q²+q+1)=78
q²+q+1=78/54=13/9
9q²+9q-4=0
D=81+144=225,√D=15
q=(-9-15)/18=-24/18=-4/3
q=(-9+15)/18=6/18=1/3
1) cos26*cos14-cos64*cos76-cos40=cos26*cos14-cos(90-26)*cos(90-14)-cos40=cos26*cos14-sin26*sin14-cos40=cos(26+14)-cos40=cos40-cos40=0;
2) sin50*cos22-sin40*cos68-sin20=sin50*cos22-sin(90-50)*cos(90-22)-sin20=sin50*cos22-cos50*sin22-sin20=sin(50-22)-sin20=sin28-sin20=2cos24*sin4.