For any positive integer n, the sine polynomials that are nonnegative in [0, π] and which have the maximal derivative at the origin are determined in an explicit form. Associated cosine polynomials K n (θ) are constructed in such a way that {K n (θ)} is a summability kernel. Thus, for each p, 1 ≤ p ≤ ∞ and for any 2π-periodic function f ∈ L p [−π, π], the sequence of convolutions K n * f is proved to converge to f in L p [−π, π]. The pointwise and almost everywhere convergences are also consequences of our construction.