容易检验n=1,2不是此方程的解,所以n≥3.当n>2时,我们有[4/(n+2)]/[3/(n+1)]=(4n+4)/(3n+6)=1+(n-2)/(3n+6)>1[4/(n+2)]/(2/n)=2n/(n+2)=1+(n-2)/(n+2)>1即方程左端三项之中4/(n+2)最大,因此4/(n+2)>(133/60)/3=133/18...