chain rule

dy/dx = d[sin(cos(tan(3x +1)))]/d[cos(tan(3x+1))] times d[cos(tan(3x+1))]/d[tan(3x +1)] times d[tan(3x+1)]/d(3x+1) times d(3x +1)/dx
= cos(cos(tan(3x+1)) times -sin(tan(3x+1)) times sec^2(3x+1) times 3
= -3[cos(cos(tan(3x+1)))][sin(tan(3x+1))][sec^2(3x+1)].