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NC
1
M
2
VA
27 tháng 7 2016
Ta có :
\(x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-..-\frac{20}{53.55}=\frac{3}{11}\)
\(x-\left(\frac{20}{11.13}+\frac{20}{13.15}+\frac{20}{15.17}+...+\frac{20}{52.55}\right)=\frac{3}{11}\)
Đặt \(A=\frac{20}{11.13}+\frac{20}{13.15}+\frac{20}{15.17}+...+\frac{20}{53.55}\)
\(A=10\left(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+...+\frac{2}{53.55}\right)\)
\(A=10\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{53}-\frac{1}{55}\right)\)
\(A=10\left(\frac{1}{11}-\frac{1}{55}\right)\)
\(A=10.\frac{4}{55}=\frac{40}{55}=\frac{8}{11}\)
=> \(x-\frac{8}{11}=\frac{3}{11}\)
\(x=\frac{3}{11}+\frac{8}{11}=\frac{11}{11}=1\)
Ủng hộ mk nha !!! ^_^
NP
4 tháng 4 2015
\(x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-...-\frac{20}{53.55}=\frac{3}{11}\)
Đặt \(A=\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-...+\frac{20}{53.55}\)
\(A=\frac{10.2}{11.13}-\frac{10.2}{13.15}-\frac{10.2}{15.17}-...-\frac{10.2}{53.55}\)
\(A=10\left(\frac{2}{11.13}-\frac{2}{13.15}-\frac{2}{15.17}-...-\frac{2}{53.55}\right)\)
\(A=10\left(\frac{1}{11}-\frac{1}{55}\right)\)
\(A=10.\frac{4}{55}\)
\(A=\frac{40}{55}\)\(A=10.\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{53}-\frac{1}{55}\right)\)
26 tháng 3 2017
x-20/11*13-20/13*15-20/15*17-......-20/53*55=3/11
x-[10*(2/11*13+2/13*15+........+2/53*55)]=3/11
x-[10*(1/11-1/13+1/13-1/15+.......1/53-1/55)]=3/11
x-[10*(1/11-1/55)] =3/11
x-(10*4/55) =3/11
x-8/11 =3/11
x =3/11+8/11
x = 1
28 tháng 2 2023
a: =-5/9-4/9+8/15+7/15-2/11=-2/11
b: =10/17+7/17-5/13-8/13+11/25
=11/25
c: =(9/12-2/12)*3/2=7/12*3/2=21/24=7/8
d: =(31/10-25/10)*3-2
=3/5*3-2
=9/5-2
=-1/5
TV
0
31 tháng 8 2018
\(x-\left(\frac{20}{11.13}+\frac{20}{13.15}+\frac{20}{15.17}+...+\frac{20}{53.55}\right)=\frac{3}{11}.\)
\(x-\frac{20}{2}.\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{53}-\frac{1}{55}\right)=\frac{3}{11}\)
\(x-10.\left(\frac{1}{11}-\frac{1}{55}\right)=\frac{3}{11}\)
\(x-10\cdot\frac{4}{55}=\frac{3}{11}\)
\(x-\frac{8}{11}=\frac{3}{11}\)
x = 1
\(2x-10\left(\frac{2}{11.13}+\frac{1}{13.15}+\frac{1}{15.17}+...+\frac{2}{53.55}\right)=\frac{3}{11}\)
\(\Leftrightarrow\)\(2x-10\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{53}-\frac{1}{55}\right)=\frac{3}{11}\)
\(\Leftrightarrow\)\(2x-10\left(\frac{1}{11}-\frac{1}{55}\right)=\frac{3}{11}\)
\(\Leftrightarrow\)\(2x-\frac{8}{11}=\frac{3}{11}\)
\(\Leftrightarrow\)\(2x=1\)
\(\Leftrightarrow\)\(x=\frac{1}{2}\)
x=\(\frac{1}{2}\)
K cho mk nha