Tinh: 1/1*2+1/2*3+1/3*4+1/4*5+1/5*6
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21 tháng 3 2017
1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6
= 1/1-1/6
=6/6-1/6
= 5/6
C
16 tháng 9 2018
\(\left(\dfrac{2}{3}-\dfrac{1}{4}+\dfrac{5}{11}\right)-\left(5-\dfrac{1}{3}-\dfrac{6}{5}\right)-\left(6-\dfrac{7}{4}+\dfrac{3}{2}\right)\)
\(=\left(\dfrac{88-33+60}{132}\right)-\left(\dfrac{75-5-18}{15}\right)-\left(\dfrac{24-7+6}{4}\right)\)
\(=\dfrac{115}{132}-\dfrac{52}{15}-\dfrac{23}{4}\)
\(=-8\dfrac{19}{55}\)
TA
9 tháng 6 2023
a, \(2\dfrac{1}{3}+4\dfrac{1}{5}+4\dfrac{1}{3}\)
\(=\dfrac{7}{3}+\dfrac{21}{5}+\dfrac{13}{3}\)
\(=\dfrac{1}{3}\left(7+13\right)+\dfrac{21}{5}\)
\(=\dfrac{20}{3}+\dfrac{21}{5}=\dfrac{100+63}{15}=\dfrac{163}{15}\)
b, \(5\dfrac{3}{4}-4\dfrac{1}{2}.3\dfrac{7}{8}\)
\(=\dfrac{23}{4}-\dfrac{9}{2}.\dfrac{31}{8}\)
\(=\dfrac{23}{4}-\dfrac{279}{16}=\dfrac{92-279}{16}=-\dfrac{187}{16}\)
c, \(1\dfrac{1}{2}.3\dfrac{2}{3}.4\dfrac{3}{4}\)
\(=\dfrac{3}{2}.\dfrac{11}{3}.\dfrac{19}{4}=\dfrac{209}{8}\)
d, \(6\dfrac{4}{5}:2\dfrac{3}{4}:1\dfrac{1}{2}\)
\(=\dfrac{34}{5}:\dfrac{11}{4}:\dfrac{3}{2}\)
\(=\left(\dfrac{34}{5}.\dfrac{4}{11}\right).\dfrac{2}{3}=\dfrac{136}{55}.\dfrac{2}{3}=\dfrac{272}{165}\)
N
21 tháng 8 2018
\(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)
\(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(\frac{1}{2}-\frac{1}{6}=\frac{1}{3}\)
SF
21 tháng 8 2018
Tính nhanh :
1/2*3 + 1/3*4 + 1/4*5 + 1/5*6
= 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6
= 1/2 - 1/6
= 6/12 - 2/12
= 4/12
= 1/3
NV
0
13 tháng 9 2017
a)1/3+1/4+2/3+3/4
=(1/3+2/3)+(1/4+3/4)
=1+1
=2.
b)1/2+1/3-1/5+1/6
=(1/2+1/3+1/6)-1/5
=1-1/5
=4/5
c)2/3x4/5+1/3x4/5
=4/5x(2/3+1/3)
=4/5x1
=4/5
d)2/3x4/5-1/3x4/5
=4/5x(2/3-1/3)
=4/5x1/3
=4/15
CM
4
20 tháng 9 2020
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(\Rightarrow A=\frac{1}{2}-\frac{1}{8}\)
\(\Rightarrow A=\frac{3}{8}\)
NH
20 tháng 9 2020
\(A=\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+...+\left(\frac{1}{7}-\frac{1}{8}\right)\)
\(A=\frac{1}{2}-\frac{1}{8}\)
\(A=\frac{3}{8}\)
BQ
2
3 tháng 7 2015
A=1/1*2+1/2*3+...+1/9*10
=1-1/2+1/2-1/3+...+1/9-1/10
=(1-1/10)+(1/2-1/2)+...+(1/9-1/9)
=(10/10-1/10)+0+...+0=9/10
L
0
1/1*2+1/2*3+1/34+1/4*5+1/5*6
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6
=1-1/6
=5/6
Bài này là toán lớp 6 mà
=1-1/2+1/2-1/3+...+1/5-1/6
=1-1/6
=5/6