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问题: a,b为实数,且a+b=1,求证1/(a+1)+1/(b+1)<3/2

解答:

1/(a+1)+1/(b+1)
={(a+1)+(b+1)}/{(a+1)*(b+1)}
={(a+b)+2}/{ab+a+b+1}
=3/(ab+2)
ab+2>2
1/(a+1)+1/(b+1)<3/2