X → 0, f (x) = x-sinx is the infinitesimal of higher order g (x) = xsinx We hope to divide f (x) and G (x) to get the form of the ratio of two infinitesimals, that is, the type of 0:0, and then judge their infinitesimal relationship from the simplified result, which may involve the equivalent infinitesimal transformation

X → 0, f (x) = x-sinx is the infinitesimal of higher order g (x) = xsinx We hope to divide f (x) and G (x) to get the form of the ratio of two infinitesimals, that is, the type of 0:0, and then judge their infinitesimal relationship from the simplified result, which may involve the equivalent infinitesimal transformation

Knowing SiNx = x-x ^ 3 / 3! + O (x ^ 3) from Taylor formula
So f (x) = x-sinx = x ^ 3 / 6 + O (x ^ 3)
When x → 0, f (x) is the third order infinitesimal of X, and G (x) ~ x ^ 2 is the second order infinitesimal of X. therefore, f (x) is the higher order infinitesimal of G (x)