0a/20 0 0a/20δx1「ay/2 a/200δ aSx/2 000‖|z 0 0 /20‖|x aox a/2006y a6x/2 0006z0 / 2 0 / 2 0 0 0 0 0 ij a a a     = −      0 / 2 0 / 2 / 2 0 0 / 2 0 0 0 0 ij j a x a y s x a y a x z                   = =                   0 / 2 0 / 2 / 2 0 0 / 2 0 0 0 0 ij j a x a y a x a y a x z                   = − = −                   3) 4) 5)