In this paper we obtain the best approximation constant of function f(x)(∈C<sub>2π</sub>)by theJackson’s type operator J<sub>π3</sub>(f;x),i.e.‖J<sub>n,3</sub>
The Lebesgue constant associated with interpolation at nodes U is evaluated in this noteThe main result is an improvement on the estimate obtained by Brutman