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\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right).462-\frac{17}{x+1,05}=19.\)
\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{21}\right)462-\frac{17}{x+1,05}=19\)
\(\Leftrightarrow20-\frac{17}{x+1,05}=19\)
\(\Leftrightarrow1-\frac{17}{x+1,05}=0\)
\(\Leftrightarrow x+1,05=17\)
\(\Leftrightarrow x=15,95\)
Đặt \(A=\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\)
\(A=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{14}+...+\frac{1}{19}-\frac{1}{21}\)
\(A=\frac{1}{11}-\frac{1}{21}=\frac{10}{231}\)
thay A vào ta được:
\(\frac{10}{231}-x+\frac{23}{231}=\frac{5}{77}\)
\(x+\frac{23}{231}=\frac{10}{231}-\frac{5}{77}=-\frac{5}{231}\)
\(x=-\frac{5}{231}-\frac{23}{231}=\frac{-4}{33}\)
\(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}-x+\frac{23}{231}=\frac{5}{77}\)\(\frac{5}{77}\)
=>\(\frac{1}{11}-\frac{1}{21}-x+\frac{23}{231}=\frac{5}{77}\)
=>\(\frac{10}{231}+\frac{23}{231}-x=\frac{5}{77}\)
=>\(\frac{33}{231}-x=\frac{5}{77}\)
=>\(\frac{1}{7}-x=\frac{5}{77}\)
=>\(\frac{11}{77}-x=\frac{5}{77}\)
=>\(x=\frac{11}{77}-\frac{5}{77}=\frac{6}{77}\)
Vậy \(x=\frac{6}{77}\)
2/11.13+2/13.15+...+2/19.21x+23/231=5/77
1/11-1/13+1/13-1/15+...+1/19-1/21x+23/231=5/77
1/11+(-1/13+1/13)+(-1/15+1/15)+...+(-1/19+1/19)-1/21x+23/231=5/77
1/11+0+0+0+...+0-1/21x+23/231=5/77
1/11-1/21x+23/231=5/77
21/231-11/231x+23/231=5/77
10/231x+23/231=5/77
10/231x =5/77-23/231
10/231x =15/231-23/231
10/231x =(-8)/231
x =-8/231:10/231
x =-4/5
vậy x=-4/5
ở trên mình tính lộn.nhớ ****
\(\left(x+3\right):8+\left(\frac{1}{11}-\frac{1}{29}\right).319=19\)
\(\left(x+3\right):8+\frac{18}{319}.319=19\)
\(\left(x+3\right):8+18=19\)
\(\left(x+3\right):8=1\)
\(x+3=\frac{1}{8}\)
\(x=\frac{-23}{8}\)
Vậy \(x=\frac{-23}{8}\)
Tuy bạn đã trả lời nhưng mk ko hiểu j hết