摘要
Denoteby <sub>n</sub>（f） the degree of copositive approximation to f（x） by polynomials of degree≤n. For function f（x） ∈ C<sup>k</sup>[-1, 1] which alternates in sign finitely many timesin [-1, 1], the author obtains the following Jackson type estimates<sub>n</sub>（f）≤Cn<sup>-k</sup>w(f<sup>k</sup>, 1/n)foa any positive integer k.
Denoteby _n(f) the degree of copositive approximation to f(x) by polynomials of degree≤n. For function f(x) ∈ C^k[-1, 1] which alternates in sign finitely many timesin [-1, 1], the author obtains the following Jackson type estimates _n(f)≤Cn^(-k)w(f^(k), 1/n) foa any positive integer k.
