Chứng minh rằng: A = 1/12 + 1/13 + 1/14 + ... + 1/22 > 1/2
Giải thích
A=112+113+114+...+122>12⇔112+113+114+...+122>1122⇔112−122+113−122+114−122+...+122−122>0
Vì 112>0,113>0,...,121>122 nên 112−122>0,113−122>0,...,121−122>0,122−122=0
Suy ra A>12
A=112+113+114+...+122>12⇔112+113+114+...+122>1122⇔112−122+113−122+114−122+...+122−122>0
Vì 112>0,113>0,...,121>122 nên 112−122>0,113−122>0,...,121−122>0,122−122=0
Suy ra A>12