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Ta có \(M=\frac{1}{125\cdot2^3}\cdot\frac{1}{125\cdot3^3}\cdot\frac{1}{125\cdot4^3}\cdot...\cdot\frac{1}{125\cdot20^3}\)
\(\Rightarrow M=0\)
\(N=\frac{-1^2}{1.2}.\frac{-2^2}{2.3}.\frac{-3^2}{3.4}....\frac{-100^2}{100.101}.\frac{-101^2}{101.102}\)
\(=\frac{1}{1.2}.\frac{2.2}{2.3}.\frac{3.3}{3.4}....\frac{100.100}{100.101}.\frac{101.101}{101.102}\)
\(=\frac{1.2.2.3.3....100.100.101.101}{1.2.2.3.3.4....100.101.101.102}\)
\(=\frac{1}{102}\)
bài này không khó. Nhưng đánh máy để giải cho bạn thì thực sự khó
\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+.........+\frac{1}{99.100}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}+....+\frac{1}{99}-\frac{1}{100}\)
\(A=\frac{1}{2}-\frac{1}{100}\)
\(A=\frac{49}{100}\)
\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+.........+\frac{1}{99.100}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}+....+\frac{1}{99}-\frac{1}{100}\)
\(A=\frac{1}{2}-\frac{1}{100}\)
\(A=\frac{49}{100}\)
A=1/1x2 +1/2x3 +... +1/18x19 + 1/19x20
Nhận xét 1/1x2 = 1/1 -1/2 ; 1/2x3=1/2-1/3; ... ;1/18x19=1/18-1/19 ; 1/19x20=1/19-1/20
ta có A=1/1 - 1/2 + +1/2 -1/3+1/3- +1/18-1/19+1/19-1/20
A=1/1 - 1/20
A=20/20 - 1/20
A=(20-1)/20
A=19/20
Vậy A=19/20
A =\(\frac{1}{1.2}\)+\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+ ...+\(\frac{1}{18.19}\)+\(\frac{1}{19.20}\)
A = 1 - \(\frac{1}{2}\)+\(\frac{1}{2}\)- \(\frac{1}{3}\)+\(\frac{1}{3}\)- \(\frac{1}{4}\)+....+\(\frac{1}{18}\)- \(\frac{1}{19}\)+ \(\frac{1}{19}\)- \(\frac{1}{20}\)
A = 1 - \(\frac{1}{20}\)( Vì đã triệt tiêu )
A = \(\frac{19}{20}\)
a=(1/1-1/2) + (1/2 +1/3) +(1/3+1/4)+........+(1/2016+1/2017)
a=1/1-1/2+1/2-1/3+1/3-1/4+ ........+2016-2017
a=1/1+1/2017 =2017-1/2017
a=2016/2017
chac chan 100% do ban .tk mk nha
=19/20
=2-1/1.2+3-2/2.3+4-3/3.4+...+19-18/18.19+20-19/19.20
=2/1.2-1/1.2+2/2.3-3/2.3+.....+20/19.20-19/19.20
=1-1/2+1/2-1/3+1/3-1/4+...+1/19-1/20
=1-1/20
=19/20
A=19/20
don gian ma
<br class="Apple-interchange-newline"><div id="inner-editor"></div>11.2 +12.3 +13.4 + ...+118.19 +119.20
A = 1 - 12 +12 - 13 +13 - 14 +....+118 - 119 + 119 - 120
A = 1 - 120 ( Vì đã triệt tiêu )
A =
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{18\cdot19}+\frac{1}{19\cdot20}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}+...+\frac{1}{19}-\frac{1}{20}\)
\(=\frac{1}{1}-\frac{1}{20}\)( đã xóa những phân số giống nhau )
\(=\frac{19}{20}\)
Ta có:
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{18.19}+\frac{1}{19.20}\)
\(\Rightarrow A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{18}-\frac{1}{19}+\frac{1}{19}-\frac{1}{20}\)
\(\Rightarrow A=\frac{1}{1}-\frac{1}{20}=\frac{19}{20}\)
đụ mạ mi