12月JJ 一道题目求解

sunnylee

29.Is (a+b)/(c+d) < a/c+b/d?

1) a,b,c,d all positive

2) a,b,c,d all none zero a+c not equal to 0

sunnylee

同意

小精灵

(a+b)/(c+d) < a/c+b/d is equal to -(ad²+bc²)/[cd(c+d)]<0,

in 1), it is sufficient, but 2) is not.

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