[請益] 高一數學證明
a,b 均為實數 證明 |a+b|<= |a|+|b|
|a+b|^2 =(a+b)^2 = a^2 + 2ab + b^2 --------(A)
(|a|+ |b|)^2 = |a|^2 +2|a||b|+ |b|^2
= a^2 + 2|ab| +b^2 -------(B)
比較(A) (B) ab <= |ab| <-----如何證明???
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