已知：a=½m-2n+1,b=½m-2n+3,c=½m-2n+2.求值:a方+b方+c方-ab-ac-bc.
问题描述：
已知：a=½m-2n+1,b=½m-2n+3,c=½m-2n+2.求值:a方+b方+c方-ab-ac-bc.
答
a-b=-2,b-c1,c-a=1a方+b方+c方-ab-ac-bc=(1/2)[a^2+b^2-2ab+b^2+c^2-2bc+c^2+a^2-2ac]=((1/2)[(a-b)^2+(b-c)^2+(c-a)^2]=(1/2)[4+1+1]=(1/2)6=3a方+b方+c方-ab-ac-bc的值为3.