Đáp án:
`x= 4459/115 `
Giải thích các bước giải:
` 7/x + 4/(13.17) + 4/(17.21) + 4/(21.25) + ... + 4/(45.49) = 151/637`
`7/x + ( 1/13 - 1/17 + 1/17 - 1/21 +...+1/45 - 1/49) = 151/637`
` 7/x + ( 1/13 - 1/49 ) = 151/637 `
` 7/x + 36/637 = 151/637 `
` 7/x= 151/637 - 36/637`
`7/x= 115/637`
` x . 115 = 7 . 637 `
`x.115 = 4459 `
`x = 4459 : 115 `
`x= 4459/115 `