Tính nhanh tổng sau:
A=1/3+1/6+1/10+1/15+1/21+1/28
B=1/5.7+1/7.9+1/9.11+....+1/23.25
Những câu hỏi liên quan
Tính tổng 101 số hạng đầu tiên của dãy sau:
1/3.5 ; 1/5.7 ; 1/7.9 ; 1/ 9.11 ; ...
\(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+...+\dfrac{1}{203.205}\)
\(=\dfrac{1}{2}.\left(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{203.205}\right)\)
\(=\dfrac{1}{2}.\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{203}-\dfrac{1}{205}\right)\)
\(=\dfrac{1}{2}.\left(\dfrac{1}{3}-\dfrac{1}{205}\right)\)
\(=\dfrac{1}{2}.\dfrac{202}{615}\)
\(=\dfrac{101}{615}\)
Chúc bạn học tốt!
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Tính nhanh:1. dfrac{1}{15}+ dfrac{1}{35}+ dfrac{1}{63}+ dfrac{1}{99}+ dfrac{1}{143}2. dfrac{5}{1.3}+ dfrac{5}{1.5}+ dfrac{5}{5.7}+ dfrac{5}{7.9}+ dfrac{5}{9.11}
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Tính nhanh:
1. \(\dfrac{1}{15}\)+ \(\dfrac{1}{35}\)+ \(\dfrac{1}{63}\)+ \(\dfrac{1}{99}\)+ \(\dfrac{1}{143}\)
2. \(\dfrac{5}{1.3}\)+ \(\dfrac{5}{1.5}\)+ \(\dfrac{5}{5.7}\)+ \(\dfrac{5}{7.9}\)+ \(\dfrac{5}{9.11}\)
1: \(=\dfrac{1}{2}\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{11}-\dfrac{1}{13}\right)\)
=1/2*10/39
=5/39
2: \(=\dfrac{5}{2}\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{9}-\dfrac{1}{11}\right)=\dfrac{5}{2}\cdot\dfrac{10}{11}=\dfrac{50}{22}=\dfrac{25}{11}\)
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Câu 1:
a) Tính giá trị biểu thức sau: A=(-1).(-1)^2.(-1)^3.(-1)^4.....(-1)^2010.(-1)^2011
b)Tính nhanh: B= 13/3+13/3.5+13/5.7+13/7.9+13/9.11+13/11.13
Giúp mình với nhaa!!! Thanks mn!!!
Tính
A= 512 - 512/2 - 512/2^2 - 512/2^3 - ....- 512/210
E= 1 - 1/10 - 1/15 - 1/3 - 1/28 - 1/6 - 1/21
C= 11/1.3 + 47/3.5 + 107/5.7 + 191/7.9 +...+ 971/17.19
sai bet thang ngu nhu cho
Dấu chấm là nhân nhé !
Tính tổng:
A= 1/2+1/4+1/8+1/16
B= 75/100+18/21+19/32+1/4+3/21+13/32
C= 2/3.5+2/5.7+2/7.9+...+2/41.43
D= 1/10+1/15+1/21+...+1/120
Thanks
A= 1/3.5 + 1/5.7 + 1/7.9 + 1/9.11 +...+1/99.101
\(A=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{99.101}\)
\(\Rightarrow2A=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}...+\frac{2}{99.101}\)
\(\Rightarrow2A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{99}-\frac{1}{101}\)
\(\Rightarrow2A=\frac{1}{3}-\frac{1}{101}\)
\(\Rightarrow2A=\frac{101}{303}-\frac{3}{303}\)
\(\Rightarrow2A=\frac{98}{303}\)
\(\Rightarrow A=\frac{98}{303}:2=\frac{98}{303.2}=\frac{98}{606}=\frac{49}{303}\)
lên 820 điểm hỏi đáp nha
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B=1/3.5+1/5.7+1/7.9+....+1/21.23+1/23.25
\(2B=2\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{23}-\frac{1}{25}\right)\)
\(2B=2\left(\frac{1}{3}-\frac{1}{25}\right)\)
\(2B=2\times\frac{22}{75}\)
\(B=\frac{44}{75}\)
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1. Tính một cách hợp lí nhất:
a) 1/5.7 + 1/7.9 + 1/9.11 + ... + 1/97. 99
b) 1/5 + 1/52 + ... + 1/52017
c) 1/10 + 1/15 + 1/21 + ... + 1/120
d)(1/2 + 1)x(1/3 + 1)x(1/4 + 1)x ... (1/99 + 1)
e) 3/22 x 8/32 x 15/42 x ... x (1/99 + 1)
Mọi người giúp mik vs nhé. Mik đang cần gấp! Ai nhanh mik tick cho.
( 1/1.3+1/3.5+1/5.7+1/7.9+1/9.11). X = 2/3
\(\text{Ta có:}\) \(\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\right).x=\frac{2}{3}\)
\(\Leftrightarrow2.\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\right).x=\frac{2}{3}.2\)
\(\Leftrightarrow\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right).x=\frac{4}{3}\)
\(\Leftrightarrow\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+.....+\frac{1}{9}-\frac{1}{11}\right).x=\frac{4}{3}\)
\(\Leftrightarrow\left(1-\frac{1}{11}\right)x=\frac{4}{3}\)
\(\Leftrightarrow\frac{10}{11}x=\frac{4}{3}\)
\(\Leftrightarrow x=\frac{4}{3}:\frac{10}{11}=\frac{22}{15}\)
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