爱因斯坦惯例 凡有重复下标的即要取和, f为自由指标,/为取和指标 X (1) ik wk ∑x2=∑ x22 (2) 证明变换为正交变换 ∑x=∑∑4a=∑∑∑(qxx ij"j ik k (3) 0i≠j 又∑xx=2xx<→xx=xx1=6xx…(4)爱因斯坦惯例 (1) i ij j x a x  = ( ) i ik k il l x a x a x  = = (2) i i i i x x x x =   ( ) 3 3 3 3 3 3 3 1 1 1 1 1 1 1 i i ij j ik k ij ik j k i i j k i j k x x a x a x a a x x = = = = = = =    = =              3 1 i ij j j x a x =  =  3 3 2 2 1 1 i i i i x x = =  =  机动 目录 上页 下页 返回 结束 (4) i i j j jk j k x x x x x x = =  (3) i i ij j ik k x x a x a x = 凡有重复下标的即要取和， i为自由指标, j为取和指标．   = = = = 3 1 3 1 3 j j k 1 j j j k j k 又 x x  x x 证明变换为正交变换 1 0 i j ij i j   = =   