A=1/2^2+1/3^2+.........+1/2018^2.CTR A khong phai la so tu nhien
Những câu hỏi liên quan
CMR 1/2+1/3 +1/4 +...+1/16 khong phai la so tu nhien
chung minh rang A = 1/2 + 1/3 + 1/4 +...+ 1/50 khong phai la so tu nhien
cho a =1/2^2 +1/2^3 +1/2^4+.....+1/2^100 c/m A khong phai la so tu nhien
CAC BAN GIUP MINH GIAI NHE! AI GIAI DUNG MINH TICH CHO
chung minh C =49/1 +48/2 +...+2/48 +1/49 khong phai la so tu nhien
s=1/2+1/3=1/4=1/5=1/6=1/7=1/8co phai la so tu nhien khong? vi sao ?
chung minh rang tong sau khong phai la so tu nhien
1/2+1/3+1/4+1/5+1/6+...+1/16
Ta có:
A = (1/2 + 1/3 + 1/4 + 1/5) + (1/6 + 1/7 +1/8) + (1/9 + 1/10 + 1/11) +
(1/12 + 1/13 + 1/14) + (1/15 + 1/16) <
(1/2 + 1/3 + 1/4 + 1/5) + 3(1/6) + 3(1/9) + 3(1/12) + 3(1/15) =
2(1/2 + 1/3 + 1/4 + 1/5) < 2(1/2 + 1/2 + 1/4 + 1/4) = 3
Mặt khác
A = (1/2 + 1/3 + 1/4) + (1/5 + 1/6 + 1/7 + 1/8) + (1/9 + 1/10 + 1/11 + 1/12) +
(1/13 + 1/14 + 1/15 + 1/16)>
(1/2 + 1/3 + 1/4) + 4(1/8) + 4(1/12) + 4(1/16) =
2(1/2 + 1/3 + 1/4) > 2(1/2 + 1/4 + 1/4) = 2 => 2 < A < 3
Vậy A không là số tự nhiên
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