tìm x biết: x + 1/2 + 1/6 + 1/12 + 1/20 + 1/30 = 47/42

tìm x biết: x + 1/2 + 1/6 + 1/12 + 1/20 + 1/30 = 47/42

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  1. x + $\frac{1}{2}$ + $\frac{1}{6}$ + $\frac{1}{12}$ + $\frac{1}{20}$ + $\frac{1}{30}$ = $\frac{47}{42}$

    x + ($\frac{1}{1.2}$ + $\frac{1}{2.3}$ + $\frac{1}{3.4}$ + $\frac{1}{4.5}$ + $\frac{1}{5.6}$) = $\frac{47}{42}$

    x + (1 – $\frac{1}{2}$ + $\frac{1}{2}$ – $\frac{1}{3}$ +…+ $\frac{1}{5}$ – $\frac{1}{6}$) = $\frac{47}{42}$

    x + ( 1 – $\frac{1}{6}$) = $\frac{47}{42}$

    x + $\frac{5}{6}$ = $\frac{47}{42}$

    x = $\frac{47}{42}$ – $\frac{5}{6}$ 

    x = $\frac{2}{7}$             

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  2. x+$\frac{1}{2}$+$\frac{1}{6}$+$\frac{1}{12}$+$\frac{1}{20}$+$\frac{1}{30}$=$\frac{47}{42}$

    x+($\frac{1}{1.2}$+$\frac{1}{2.3}$+$\frac{1}{3.4}$+$\frac{1}{4.5}$+$\frac{1}{5.6}$)=$\frac{47}{42}$

    x+(1-$\frac{1}{2}$+$\frac{1}{2}$-$\frac{1}{3}$+$\frac{1}{3}$-$\frac{1}{4}$+$\frac{1}{4}$-$\frac{1}{5}$+$\frac{1}{5}$-$\frac{1}{6}$)=$\frac{47}{42}$

    x+(1-$\frac{1}{6}$)=$\frac{47}{42}$

    x+$\frac{5}{6}$=$\frac{47}{42}$

    x=$\frac{47}{42}$-$\frac{5}{6}$

    x=$\frac{2}{7}$

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