Câu hỏi của Đặng Ngọc Anh

Question

tìm X: 3 x [1/5x8 + 1/8x11 + 1/11x14 + ... + 1/97x100 + X] = 319/100

Xyz OLM · Accepted Answer

$3\times\left(\frac{1}{5\times8}+\frac{1}{8\times11}+....+\frac{1}{97\times100}+x\right)=\frac{319}{100}$$\Rightarrow\left(\frac{3}{5\times8}+\frac{3}{8\times11}+\frac{3}{11\times14}+...+\frac{3}{97\times100}\right)+3\times x=\frac{319}{100}$$\Rightarrow\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{97}-\frac{1}{100}+3\times x=\frac{319}{100}$$\Rightarrow\frac{1}{5}-\frac{1}{100}+3\times x=\frac{319}{100}$$\Rightarrow\frac{19}{100}+3\times x=\frac{319}{100}$$\Rightarrow3\times x=\frac{319}{100}-\frac{19}{100}$$\Rightarrow3\times x=3$$\Rightarrow x=3:3$$\Rightarrow x=1$Vậy x = 1Câu trả lời: $3\times\left(\frac{1}{5\times8}+\frac{1}{8\times11}+....+\frac{1}{97\times100}+x\right)=\frac{319}{100}$$\Rightarrow\left(\frac{3}{5\times8}+\frac{3}{8\times11}+\frac{3}{11\times14}+...+\frac{3}{97\times100}\right)+3\times x=\frac{319}{100}$$\Rightarrow\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{97}-\frac{1}{100}+3\times x=\frac{319}{100}$$\Rightarrow\frac{1}{5}-\frac{1}{100}+3\times x=\frac{319}{100}$$\Rightarrow\frac{19}{100}+3\times x=\frac{319}{100}$$\Rightarrow3\times x=\frac{319}{100}-\frac{19}{100}$$\Rightarrow3\times x=3$$\Rightarrow x=3:3$$\Rightarrow x=1$Vậy x = 1

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