lim(x->0-) ln(1 + ax³)/(x - arcsinx)
= lim(x->0-) 3ax²/{[1-1/√(1-x²)](1+ax³)} 0-) 2x/[3ax²(1-1/√(1-x²)-x(ax³+1)/(1-x²)^(3/2)] 0-) 1/[3ax(1-1/√(1-x²)-(ax³+1)/(1-x²)^(3/2)]