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Question

tính tổng$M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}$

bảo nam trần · Accepted Answer

$M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}$$M=\frac{2}{30}+\frac{2}{42}+...+\frac{2}{1980}$$M=2\left(\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{44.45}\right)$$M=2\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{44}-\frac{1}{45}\right)$$M=2\left(\frac{1}{5}-\frac{1}{45}\right)$$M=2\times\frac{8}{45}$$M=\frac{16}{45}$Câu trả lời: $M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}$$M=\frac{2}{30}+\frac{2}{42}+...+\frac{2}{1980}$$M=2\left(\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{44.45}\right)$$M=2\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{44}-\frac{1}{45}\right)$$M=2\left(\frac{1}{5}-\frac{1}{45}\right)$$M=2\times\frac{8}{45}$$M=\frac{16}{45}$

Phương An · Answer

$M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}$$M=\frac{1\times2}{15\times2}+\frac{1\times2}{21\times2}+\frac{1\times2}{28\times2}+\frac{1\times2}{946\times2}+\frac{1\times2}{990\times2}$$M=\frac{2}{30}+\frac{2}{42}+\frac{2}{56}+...+\frac{2}{1892}+\frac{2}{1980}$$M=2\times\left(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+...+\frac{1}{1892}+\frac{1}{1980}\right)$$M=2\times\left(\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+...+\frac{1}{43\times44}+\frac{1}{44\times45}\right)$$M=2\times\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\right)$$M=2\times\left(\frac{1}{5}-\frac{1}{45}\right)$$M=2\times\left(\frac{9}{45}-\frac{1}{45}\right)$$M=2\times\frac{8}{45}$$M=\frac{16}{45}$Chúc bạn học tốtCâu trả lời: $M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}$$M=\frac{1\times2}{15\times2}+\frac{1\times2}{21\times2}+\frac{1\times2}{28\times2}+\frac{1\times2}{946\times2}+\frac{1\times2}{990\times2}$$M=\frac{2}{30}+\frac{2}{42}+\frac{2}{56}+...+\frac{2}{1892}+\frac{2}{1980}$$M=2\times\left(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+...+\frac{1}{1892}+\frac{1}{1980}\right)$$M=2\times\left(\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+...+\frac{1}{43\times44}+\frac{1}{44\times45}\right)$$M=2\times\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\right)$$M=2\times\left(\frac{1}{5}-\frac{1}{45}\right)$$M=2\times\left(\frac{9}{45}-\frac{1}{45}\right)$$M=2\times\frac{8}{45}$$M=\frac{16}{45}$Chúc bạn học tốt

Hoàng Phúc · Answer

$\frac{M}{2}=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+....+\frac{1}{940}+\frac{1}{990}$$\frac{M}{2}=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+....+\frac{1}{1892}+\frac{1}{1980}$$\frac{M}{2}=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+......+\frac{1}{43.44}+\frac{1}{44.45}$$\frac{M}{2}=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}$$\frac{M}{2}=\frac{1}{5}-\frac{1}{45}=\frac{8}{54}=>M=\frac{8}{45}.2=\frac{16}{45}$Vậy M=16/45Câu trả lời: $\frac{M}{2}=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+....+\frac{1}{940}+\frac{1}{990}$$\frac{M}{2}=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+....+\frac{1}{1892}+\frac{1}{1980}$$\frac{M}{2}=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+......+\frac{1}{43.44}+\frac{1}{44.45}$$\frac{M}{2}=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}$$\frac{M}{2}=\frac{1}{5}-\frac{1}{45}=\frac{8}{54}=>M=\frac{8}{45}.2=\frac{16}{45}$Vậy M=16/45

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