On Best Polynomial Approximation in L2W(S)

The best polynomial approximation is estimated by appropriate K-functionals in L2w(S) where w(x) is a Jacobi-type weight and S is a simplex (or prism). For Lpw[−1,1] the best polynomial approximation will be estimated for wλ(x) = (1 − x2)λ−1/2 and (2λ + 1)/(λ + 1) < p < (2 λ + 1)/λ.