CtR : 1/5+1/15+1/25+1/41+1/6+1/85+1/113 <1/2
Những câu hỏi liên quan
CtR : 1/5+1/15+1/25+1/41+1/6+1/85+1/113 <1/2
CtR : 1/5+1/15+1/25+1/41+1/6+1/85+1/113 <1/2
CtR : 1/5+1/15+1/25+1/41+1/6+1/85+1/113 <1/2
de sai ban oi to thu may tinh do nghe
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so sanh 1/2 va 1/5 + 1/13 + 1/25 + 1/41 + 1/85 + 1/113
CMR: 1/5+1/13+1/25+1/41+1/61+1/85+1/113<1/2
chung to : 1/5 + 1/16 + 1/25 + 1/41 + 1/60 + 1/85 + 1/113 < 1/2
so sánh A=1/5+1/13+1/25+1/41+1/61+1/85+1/113 với 1/2
chứng tỏ: a, 1/5 + 1/6 + 1/7 + .... + 1/17 < 2
b, 1/5 + 1/13 + 1/25 + 1/41 + 1/61 + 1/85 + 1/113 < 1/2
a, 1/5+1/6+1/7+1/8+1/9 < 1/5.5=1 (1)
1/10+1/11+1/12+1/13+1/14+1/15+1/16+1/17 < 1/10.7 < 1/10.10 < 1 (2)
Từ (1) và (2) , suy ra 1/5+1/6+1/7+...+1/17 < 1+1 =2
Suy ra , 1/5+1/6+1/7+...+1/17 < 2
b, Ta cần c/m 1/13+1/25+1/41+1/61+1/85+1/113 < 3/10 (Vì 1/2 - 1/5 = 3/10)
1/13+1/25+1/41+1/61+1/85+1/113 < 1/10+1/25+1/25+1/25+1/25+1/25
1/13+1/25+1/41+1/61+1/85+1/113 < 1/10 + 5/25 = 1/10+1/5 = 3/10
Suy ra , 1/5+1/13+1/25+1/41+1/61+1/85+1/113 < 1/2
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1- ( 1/5 +1/13+1/25+1/41+1/61+1/85+1/113)
So sánh với 1/2.