A new superconvergence and extrapolation for second order triangular element

In this paper, we find a new superconvergence and extrapolation for second order triangular element based on [W.-m. He, J.-z. Cui, Q.-d. Zhu, An improved method on superconvergence and extrapolation, Math. Numer. Sinica 24 (2002) 3 (in Chinese)]. Of course, some numerical examples are given to investigate those estimates.