let, y=3x1+2x4
differentiating on both sides w.r.t x
dydx=3(1+2x4)−(3x)(x3)(1+2x4)
(∵(f(x)g(x))dx=f′(x)g(x)−g′(x)f(x)(g(x))2)
=3−6x4−24x4(1+2x4)2
dydx=3−18x4(1+2x4)2