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C=5/1.2+5/2.3+5/3.4+...+5/99.100
C=5.(1/1.2+1/2.3+1/3.4+...+1/99.100)
C=5.(1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100)
C=5.(1-1/100)
C=5.(100/100-1/100)
C=5.9/100
C=9/20
Chúc bạn học tốt nha, Lan Anh
\(C=\frac{5}{1.2}+\frac{5}{2.3}+\frac{5}{3.4}+....+\frac{5}{99.100}\)
\(C=5.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+......+\frac{1}{99.100}\right)\)
\(C=5.\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+......+\frac{1}{99}-\frac{1}{100}\right)\)
\(C=5.\left(\frac{1}{1}-\frac{1}{100}\right)=5.\frac{99}{100}=\frac{99}{20}\)
Vậy C=99/20
5 . 3 - 5 . x - 2 . x - 2 . 4 = -4
15 - 5 . x - 2 .x -8 =-4
15 - 5 .x - 2. x = -4 + 8
15 - 5 . x -2 . x = 4
5 . x - 2 .x = 15 - 4
x.( 5 - 2) =9
x. 3 9
x = 9 /3
x =3
\(\frac{10}{3}x+\frac{67}{4}=-\frac{53}{4}\)
<=> \(\frac{10}{3}x=-30\)
=> x = -9
1) \(x^2+\frac{8}{9}=\frac{41}{36}\)\(\Leftrightarrow x^2=\frac{1}{4}\Leftrightarrow x=\pm\frac{1}{2}\)
2) \(\left(x-3\right)^2+-\frac{9}{25}=\frac{2}{5}.\frac{8}{5}\)
\(\Leftrightarrow\left(x-3\right)^2=1\)
\(\Leftrightarrow\orbr{\begin{cases}x-3=1\\x-3=-1\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=4\\x=2\end{cases}}\)
3) \(\frac{3}{11}.\frac{22}{6}-\left(x-1\right)^2=\frac{7}{16}\)
\(\Leftrightarrow\left(x-1\right)^2=\frac{9}{16}\)
\(\Leftrightarrow\orbr{\begin{cases}x-1=\frac{3}{4}\\x-1=-\frac{3}{4}\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{7}{4}\\x=\frac{1}{4}\end{cases}}\)
4) \(1+\left(x+1\right)^3=\frac{37}{64}\)
\(\Leftrightarrow\left(x+1\right)^3=-\frac{27}{64}\)
\(\Rightarrow x+1=-\frac{3}{4}\)
\(\Leftrightarrow x=-\frac{7}{4}\)
5) \(\left(x-\frac{1}{2}\right)^2-\frac{9}{16}=1\)
\(\Leftrightarrow\left(x-\frac{1}{2}\right)^2=\frac{25}{16}\)
\(\Leftrightarrow\orbr{\begin{cases}x-\frac{1}{2}=\frac{5}{4}\\x-\frac{1}{2}=-\frac{5}{4}\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{7}{4}\\x=-\frac{3}{4}\end{cases}}\)
6) Bn ghi rõ đề nha mk ko hiểu
6 ) \(\frac{3-x}{5-x}=\left(\frac{-3}{5}\right)^2\)
\(\frac{3-x}{5-x}=\frac{9}{25}\Leftrightarrow\frac{3-x}{5-x}-\frac{9}{25}\Leftrightarrow\frac{75-25x}{125-25x}-\frac{45-9x}{125-5x}=0\)
\(\Rightarrow\frac{75-25-45+9x}{125-25x}=0\Leftrightarrow5+9x=0\Leftrightarrow x=\frac{-5}{9}\)
\(\frac{2}{3}x:\frac{1}{5}=\frac{4}{3}:25\%\)
\(\frac{2}{3}x:\frac{1}{5}=\frac{4}{3}:\frac{1}{4}=\frac{16}{3}\)
\(\frac{2}{3}x=\frac{16}{3}.\frac{1}{5}=\frac{16}{15}\)
\(x=\frac{16}{15}:\frac{2}{3}=\frac{8}{5}\)
Vậy x=8/5
dễ nhưng dài