`1/(3xx5) + 1/(5 xx 7) + 1/( 7 xx9) + .... + 1/( x xx ( x + 2)) = 103/600`
`1/2 xx ( 2/(3xx5) + 2/(5 xx 7) + 2/( 7 xx9) + .... + 2/( x xx ( x + 2))) = 103/600`
`1/2 xx ( 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/x - 1/(x+2)) = 103/600`
`1/2 xx ( 1/3 - 1/( x+2)) = 103/600`
`1/3 - 1/(x + 2) = 103/600 : 1/2`
`1/3 - 1/(x+2) = 103/300`
`1/(x+2) = 1/3 - 103/300`
Mà `103/300 > 1/3`
⇒ `x` không tồn tại