Sharp inequalities of Jackson-Stechkin in terms of <i>τ</i>-modules of continuity in <i>L</i><sub>2</sub>
For τ modules of smoothness of m order the sharp constant in Jackson-Stechkin type inequality were calculated. Also for some classes of functions averaged with given weights of τ modules of smoothness of r derivatives which majorized with given functions the sharp upper bounds of the best joint polynomial approximation were found.