lim（x→0）[sinx-x+x^3/6]/x^5
=lim（x→0）[cosx-1+x^2/2]/(5x^4)
=lim（x→0）[-sinx+x]/(20x^3)
=lim（x→0）[1-cosx]/(60x^2)
=lim（x→0）(x^2/2)/(60x^2)
=1/120