（a-b+c-b）²-（a+b-c+d）²=（a-b+c-b+a+b-c+d）（a-b+c-b-a-b+c-d）=（2a-b+d）（-3b+2c-d）=-6ab+4ac-2ad+3b²-2bc+bd-3bd+2cd-d²=-6ab+4ac-2ad+3b²-2bc-2bd+2cd-d²
(a-b+c-b²)-(a+b-c+d²)=a-b+c-b²-a-b+c-d²=-2b+2c-b²-d²
