Let f(x)=cosx3.sin2(x5)
∴f′(x)=ddx[cosx3.sin2(x5)]=sin2(x5)×ddx(cosx3)+cosx3×ddx[sin2(x5)]
=sin2(x5)×(−sinx3)×ddx(x3)+cosx3×2sin(x5).ddx[sinx5]
=−sinx3sin2(x5)×3x2+2sinx5cosx3.cosx5×ddx(x5)
=−3x2sinx3.sin2(x5)+2sinx5cosx5cosx3×5x4
=10x4sinx5cosx5cosx3−3x2sinx3sin2(x5)