a) x+ 4/9.13 + 4/13.17 + 4//17.21 + …… + 4/41.45 = 10

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1. Câu a

    `x+ 4/(9.13) + 4/(13.17) + 4/(17.21) + …… + 4/(41.45) = 10`

   `=>x+ (4/(9.13) + 4/(13.17) + 4/(17.21) + …… + 4/(41.45) )= 10`

   `=>x+ (1/9-1/13 + 1/13-1/17 + 1/17-1/21 + …… + 1/41-1/45 )= 10`

   `=>x+ (1/9-1/45 )= 10`

   `=>x+ 4/45= 10`

   `=>x=9 41/45`

   Học tốt!!!

   #nocopy

    

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2. a.x+ $\frac{4}{9.13}$ +$\frac{4}{13.17}$ +$\frac{4}{17.21}$ +…+$\frac{4}{41.45}$=10

   ⇔x+($\frac{4}{9.13}$ +$\frac{4}{13.17}$ +$\frac{4}{17.21}$ +…+$\frac{4}{41.45}$ )=10

   ⇔x+($\frac{1}{9}$ -$\frac{1}{13}$ +$\frac{1}{13}$ -$\frac{1}{17}$ +$\frac{1}{17}$ -$\frac{1}{21}$ +…+$\frac{1}{41}$ -$\frac{1}{45}$ )=10

   ⇔x+($\frac{1}{9}$ -$\frac{1}{45}$ )=10

   ⇔x+$\frac{4}{45}$ =10

   ⇔x=10-$\frac{4}{45}$ 

   ⇔x=9$\frac{41}{45}$ .

   Vậy x=9$\frac{41}{45}$ .

    

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