已知a-b=2 b-c=1/2 求2a方;+2b方;+2c方;-2ab-2ac-2bc的值

a-b=2 b-c=1/2两式相加得a-c=2+1/2=5/22a方;+2b方;+2c方;-2ab-2ac-2bc=a^2-2ab+b^2+a^2-2ac+c^2+b^2-2bc+c^2=(a-b)^2+(b-c)^2+(a-c)^2=2^2+(1/2)^2+(5/2)^2=4+1/4+25/4=10。5