We have, f(x)=sin(ax+b)cos(cx+d)
Thus using quotient rule and chain rule simualtaneously,
f′(x)=acos(ax+b).cos(cx+d)−sin(ax+b)(−csin(cx+d))[cos(cx+d)]2
=acos(ax+b)cos(cx+d)+csin(ax+b).sin(cx+d)cos(cx+d)×1cos(cx+d)
=acos(ax+b)sec(cx+d)+csin(ax+b)tan(cx+d)sec(cx+d)