楠风拂面
幼苗
共回答了16个问题采纳率:87.5% 举报
a²+b²+c²-ab-bc-ac
=(2a²+2b²+2c²-2ab-2bc-2ac)/2
=[(a²-2ab+b²)+(a²-2ac+c²)+(b²-2bc+c²)]/2
=[(a-b)²+(a-c)²+(b-c)²]/2
=[(2005x+2006-2005x-2005)²+(2005x+2006-2005x-2007)²+(2005x+2005- 2005x+2007)²]/2
=[1²+(-1)²+(-2)²]/2
=6/2
=3
1年前
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