[toán 5] phân số

X

xuanquynh97

Biểu thức sẽ = $\dfrac{7}{1.5}+\dfrac{7}{5.9}+\dfrac{7}{9.13}$ + $\dfrac{7}{13.17}$ +$\dfrac{7}{17.21}$

$=\dfrac{7}{4}.(\dfrac{4}{1.5}+\dfrac{4}{5.9}$ +$\dfrac{4}{9.13}+\dfrac{4}{1.17}+\dfrac{4}{17.21}$

$=\dfrac{7}{4}.(1-\dfrac{1}{21})=\dfrac{5}{3}$
 
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