>>730

 (左辺) - (右辺) = a^4 +b^4 +c^4 + 2abc(a+b+c) -a^3・b -b^3・c -c^3・a
   = (1/2)(a^2 -b^2 -ab -ca)^2 + cyclic
   ≧ 0,

〔類題268〕
 (a^2 + b^2 + c^2)^2 ≧ 3(a^3・b + b^3・c + c^3・a),
>>268
>>284-290