∵(a-b)^2+(B-c)^2+(a-c)^2≥0得2a^2+2b^2+2c^2≥2ab+2ac+2bc得3a^2+3b^2+3c^2≥a^2+b^2+c^2+2ab+2ac+2bc即3(a^2+b^2+c^2)≥(a+b+c)^2等号成立时a=b=c代入a+b+c=6a^2+b^2+c^2=12得等号成立,即a=b=c...