[x+3/7]x7/3=5/2
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\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{8}{7}\times\dfrac{7}{10}\)
\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{4}{5}\)
\(x\div\dfrac{2}{3}=0\)
\(x=0\)
\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{8}{7}\cdot\dfrac{7}{10}\)
\(x\cdot\dfrac{3}{2}+\dfrac{4}{5}=\dfrac{4}{5}\)
\(x\cdot\dfrac{3}{2}=\dfrac{4}{5}-\dfrac{4}{5}=0\)
\(x=0\div\dfrac{3}{2}=0\)
Vậy x = 0
\(\Leftrightarrow y\times\left(\dfrac{1}{7}+\dfrac{9}{21}+\dfrac{7}{3}\right)=\dfrac{5}{3}\)
\(\Leftrightarrow y\times\dfrac{61}{21}=\dfrac{5}{3}\)
\(\Leftrightarrow y=\dfrac{5}{3}:\dfrac{61}{21}=\dfrac{35}{61}\)
y x (1/7 +9/21 +7/3)= 5/3
y x 61/21 = 5/3
y = 5/3 : 61/21
y= 35/61
\(B=\frac{36}{1.3.5}+\frac{36}{3.5.7}+\frac{36}{5.7.9}+...+\frac{36}{25.27.29}\)
\(=9.\left(\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+...+\frac{4}{25.27.29}\right)\)
\(=9.\left(\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+\frac{1}{5.7}-\frac{1}{7.9}+...+\frac{1}{25.27}-\frac{1}{27.29}\right)\)
\(=9.\left(\frac{1}{3}-\frac{1}{675}\right)\)
\(=9.\frac{224}{675}\)
\(=\frac{224}{75}\)
\(\left(x+\frac{3}{7}\right).\frac{7}{3}=\frac{5}{2}\)
\(x+\frac{3}{7}=\frac{5}{2}\div\frac{7}{3}\)
\(x+\frac{3}{7}=1\frac{1}{14}\)
\(x=1\frac{1}{14}-\frac{3}{7}\)
\(x=\frac{9}{14}\)
Vậy: .........
Nớ k nhé!