1楼MALIDOU
(......)
发表于 2007-10-21 21:16
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设这三个数为a,a+1,a+2(a为整数)
1:a除以3余0;
设a=3k,
则,a(a+1)(a+2)=3k(3k+1)(3k+2)
得证
2:a除以3余1
设a=3k+1,
则,a(a+1)(a+2)=(3k+1)(3k+2)(3k+3)
=3(3k+1)(3k+2)(k+1)
得证
3:a除以3余2
设a=3k+2,
则,a(a+1)(a+2)=(3k+2)(3k+3)(3k+4)
=3(3k+4)(3k+2)(k+1)
得证.