For non-negative continuous function f(x) defined on [0,1], and f≠0, the present paper proves that, there is a polynomial Pn(x)∈Πn(+), such that
|f(x)−1Pn(x)|≤Cωφλ(f,n−1/2A1−λn(x)),
where
An(
x)=\sqrt{x(1-x)}+1/\sqrt{n},\;0\leq \lambda\leq 1,
and\Pi_n(+)$ indicates the set of all polynomials of degree
n with positive coefficients. When
f(x) has exact
l sign change points in (0, 1), we also construct a rational function
r(x)∈Rln(+) such that
|f(x)−r(x)|\leqC(l+1)2ωφλ(f,n−1/2A1−λn(x)).