an≤a(n+1)a(n+1)-an≥0(n+1)²+k(n+1)-(n²+kn)≥02n+1+k≥0k≥-(2n+1)随n增大,2n+1单调递增,-(2n+1)单调递减当n=1时,-(2n+1)有最大值-(2×1+1)=-3要不等式对于任意正整数n恒成立,只需当-(2n+1)取最大值时,...