Method of hermite interpolation by polynomials of the third degree on a triangle using mixed derivatives

There is a sine of the minimum angle of the triangle in the denominator of estimation of inaccuracy of interpolation for derivative of function in building of triangular finite elements. The way of method of Hermite interpolation by polynomials of the third degree on a triangle suggested by N. V. Baidakova is free of minimum angle condition for approximation of any derivatives. There is two-dimenetional cubic element in finite element method equal to element of N. V. Baidakova in this paper. The considered estimations of inaccuracy for function derivatives in the directions up to derivative of order three in inclusive is free of triangle geometry. The unimprovable of calculated estimations of inaccuracy of approximations of derivatives in directions is proved in accuracy up to absolute constants.