a/(bc)+c/(ab)+b/(ac)-1/a-1/b-1/c
=a²/(abc)+c²/(abc)+b²/(abc)-bc/(abc)-ac/(abc)-ab/(abc)
=1/(2abc)(2a²+2c²+2b²-2bc-2ac-2ab)
=1/(2abc)(a²-2ab+b²+b²-2bc+c²+a²-2ac+c²)
=1/(2abc)[(a-b)²+(b-c)²+(a-c)²]