已知a-b=3,b-c=2,求a∧2-bc+b∧2-ac+c∧2-ab的值

∵ a - b = 3,b - c = 2
∴a - b + b - c = a - c = 5
∴a² - bc + b² - ac + c² - ab
=1/2(a² - 2ab + b² + a² - 2ac + c² + b² - 2bc + c² )
=1/2[(a - b)² + (a - c)² + (b - c)² ]
=1/2(9 + 25 + 4)
=1/2*38
=19