x->0tanx ~ x +(1/3)x^3e^(tanx) ~ 1 +[x +(1/3)x^3] + (1/2)[x +(1/3)x^3]^2~ 1+x +(1/2)x^2 +(1/3)x^3e^x ~1+x +(1/2)x^2e^(tanx) - e^x ~(1/3)x^3//lim(x->0) ( e^tanx - e^x) /x^2=lim(x->0) (1/3)x^3 /x^2=0
是高阶无穷小,具体如图