What are source of error in flat elements traiangle finite element method? How can we improve it

. Elements are flat triangular planes, nodes (x1, )1), (x2, yz), (X3, >3) at corners . Variation of (x, y) by adjusting the values p; Note: each node is usually shared between several adjacent elements Again w(x, y) = Ly(x, y) and U(y) = EU(y()) (e ) (e ) In 2d, the interpolating function describing a triangle with nodes (x1, y1, 1), (X2, y2, (2), and (X3, )3, ] N.(e) 1 2A(e) (23)1 - X1)3) + ()/3 - Vi)x - (x3 - x])y] A - area of the 1 triangle N(e) 2A(e) [(x1)2 - x2)1) + (V1 - yz)x - (x1 - x2)y]