EN
Let $f_{c}(x,y) ≡ ∑_{j=1}^{∞} ∑_{k=1}^{∞} a_{jk}(1 - cos jx)(1 - cos ky)$ with $a_{jk} ≥ 0$ for all j,k ≥ 1. We estimate the integral $∫_{0}^{π}∫_{0}^{π} x^{α-1} y^{β-1} ϕ(f_{c}(x,y)) dxdy$ in terms of the coefficients $a_{jk}$, where α, β ∈ ℝ and ϕ: [0,∞] → [0,∞]. Our results can be regarded as the trigonometric analogues of those of Mazhar and Móricz [MM]. They generalize and extend Boas [B, Theorem 6.7].