2 Ml 0 2 01 21 T21M1=721R M=RM    = − = ' 1 ' 2 1 1 ' 1 ' 2 2 1 h h u d n u n u                 − =       ' 1 ' 1 ' 1 1 ' 1 ' 1 2 2 2 2 1 1 0 h n u n d h n u 1 ' 1 ' 1 2 2 1 1 1 0 T           − = n d ' M2 = T21M1 = T21R1 M1 1 1 ' M1 = R M