同理可推导出 (6, f+b3x) =2+ 13 (a t+ay a22 aYs Z (,f+ by) a23 Zs Z (c,f+c,y)同理可推导出 ( ) 1 ( ) 1 ( ) 1 ( ) 1 ( ) 1 23 2 3 22 2 3 21 2 3 13 1 3 12 1 3 c f c y Z Z y a b f b y Z Y y a a f a y Z X y a c f c x Z Z x a b f b x Z Y x a S S S S S = +   = = +   = = +   = = +   = = +   = − − − − −