∵a+b+c=0,即a=-(b+c),b+c=-a,∴原式=1(b+c)2?b2?c2+1b2?(b+c)2?c2+1c2?(b+c)2?b2=12bc+1?2bc?2c2+1?2bc?2b2=12bc-12c(b+c)-12b(c+b)=12bc+12ac+12ab=a+b+c2abc=0.
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