a2b2c2d2abcd的精选

问题详情：已知ad-bc=1,求*:a2+b2+c2+d2+ab+cd≠1.【回答】【*】假设a2+b2+c2+d2+ab+cd=1,则2a2+2b2+2c2+2d2+2ab+2bc+2cd-2ad-2bc+2ad=2,即(a+b)2+(b+c)2+(c+d)2+(a-d)2+2ad-2bc=2,若(a+b)2+(b+c)2+(c+d)2+(a-d)2=0,则...