0:ac+cd=0ac=-cd(ac)^2=(cd)^2a^2(1-d^2)=(cd)^2整理得:a^2=(a^2+d^2)d^2 a^2=d^2 {a=d或a=-d}同理:{b=c或b=-c}又因为:ac+bd=0所以:a=d,b=-c或a=-c,b=c;故有:ab+cd=0...