Question

知a-b=2 b-c=3求a*a+b*b+c*c-ab-ac-bc值

Answer 1

a - b = 2 b - c = 3 则：a - c = 5 a*a + b*b + c*c - ab - ac - bc = a*a - ab + b*b - bc + c*c - ac = a * (a - b) + b * (b - c) + c * (c - a) = 2a + 3b - 5c = 2a - 3c + 3b - 3c = 2(a - c) + 3(b - c) = 20 + 9 = 29