Đáp án:
`2/3 x - 70 10/11 : ( 131313/151515 + 131313/353535 + 131313/636363 + 131313/999999) = -5`
`2/3 x - 780/11 : ( 13/15 + 13/35 + 13/ 63 + 13/99) =-5`
`2/3 x - 780/11 : [ 13/2 . ( 2/( 3 xx5) + 2/(5 xx 7) + 2/(7 xx 9) + 2/(9 xx 11) ) ] = -5`
`2/3 x - 780/11 : [ 13/2 . ( 1/3 - 1/11)] =-5`
`2/3 x -780/11 : [ 13/2 . 8/33] =-5`
`2/3 x -780/11 : 52/33 =-5`
`2/3 x - 45 =-5`
`2/3 x =-5 + 45`
`2/3 x =40`
` x =40 : 2/3`
`x =60`
`text{ XIN HAY NHẤT NHA}`
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