\(=1-\dfrac{1}{2}+1-\dfrac{1}{6}+1-\dfrac{1}{12}+1-\dfrac{1}{20}+1-\dfrac{1}{30}+1-\dfrac{1}{42}+1-\dfrac{1}{56}\)
\(=7-\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{56}\right)\)
\(=7-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{7}-\dfrac{1}{8}\right)\)
\(=7-\dfrac{7}{8}=\dfrac{49}{8}\)
Tính :
A= 3/2 - 5/6 +7/12 - 9/20 + 11/30 - 13/42 + 15/56 - 17/72 = 19/70
Tính:
K = \(\dfrac{1}{1.2.3.4}\)+\(\dfrac{1}{2.3.4.5}\)+......+\(\dfrac{1}{n\left(n+1\right)\left(n+2\right)}\)
M = \(\dfrac{1}{2}\) +\(\dfrac{5}{6}\)+\(\dfrac{11}{12}\)+\(\dfrac{19}{20}\)+\(\dfrac{29}{30}\)+\(\dfrac{41}{42}\)+\(\dfrac{55}{56}\)+\(\dfrac{71}{72}\)+\(\dfrac{89}{90}\)
Bài1. (4điểm) Thực hiện phép tính:
a) \(A=\dfrac{3}{5}+6\dfrac{5}{6}\left(11\dfrac{5}{20}-9\dfrac{1}{4}\right):8\dfrac{1}{3}\)
b) \(B=\dfrac{-1}{2}+\dfrac{-1}{6}+\dfrac{-1}{12}+\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)
Tính thuận tiện A=\(\dfrac{3}{2}-\dfrac{5}{6}+\dfrac{7}{12}-\dfrac{9}{20}+\dfrac{11}{30}-\dfrac{13}{42}+\dfrac{15}{56}-\dfrac{17}{72}\)
BT:
8/9 - 1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56 - 1/72 =
tính :
B= 1/90 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
Tính:
\(E=\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\)
Tính: A= 1- \(\frac{5}{6}+\frac{7}{12}-\frac{9}{20}+\frac{11}{30}-\frac{13}{42}+\frac{15}{56}-\frac{17}{72}+\frac{19}{90}\)
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Làm ơn giúp mình
Bài 1. Tính hợp lý
1) (–12) +6.(–3)
2) (36 -2020) + (2019 -136) – 27
3) (144 – 97) – (244 – 197)
4) (–24).13 – 24.( –3)
5) 54+55+56+57+58-(64+65+66+67+68)
6) 24(16 – 5) – 16(24 – 5)
7) 47.(23 + 50) – 23.(47 + 50)
8) (-31). 47 + (-31). 52 + (-31)
Bài 2: Tìm số nguyên x, biết:
1)-17-(2x-5)=-6
2) 10-2(4-3x)=-4
3)-12+3(-x+7)=-18
4)-45:[5.(-3-2x)]=3
5) x.(x+3)=0
6) (x-2).(x+4)=0
7) x.(x+1).(x-3)=0
