(u.v)´=u´v+uv´
y=(lnx).x³
u=lnx, v=x³
y´=1/x .x³ + (lnx).3x²=x²+3x²lnx=x²(1+3lnx)
x=3: y´(3)=3²(1+3ln3)=9(1+ln(3³)=9(1+ln27)
6а+4а-7-а-3=9а-7
ответ:9а-7
Cos(24)+cos(48) = 2cos(36)cos(12)
cos(84)+cos(12) = 2cos(48)cos(36)
cos(24)+cos(48)-(cos(84)+cos(12) ) = 2cos(36)(cos(12)-cos(48)) = -4cos(36)sin(30)sin(-18) = 2cos(36)sin(18) = 2cos(36)sin(36)sin(18)/sin(36) = sin(72)sin(18)/sin(36) = sin(72)cos(72)/sin(36) = (1/2)*sin(144)/sin(36) = 1/2