.与x的换算 nM xM xM mmMM∑xM1 已知x on M M M M与xi的换算 已知 xi i i i i i i i i i i i m n M x M x M m nM M x M  = = = =  i i i i i iii i i i i iii m m n MMM x n m m MMM     = = = =   