a"' + a"c + b"c - abc + b"'= ( a"' + b"' ) + ( a"c - abc + b"c )= ( a + b )( a" - ab + b" ) + c( a" - ab + b" )= ( a + b + c )( a" - ab + b" )因为 a + b + c = 0,式子就是= 0( a" - ab + b" )= 0