Đáp án:
Bài 1:
a, `5/18 - (11/36 + 5/18)`
`= 5/18 - 11/36 - 5/18`
`= (5/18 - 5/18) - 11/36`
`= -11/36`
b, `-7/13 . 2/11 + - 7/13 . 9/11 + -6/13`
` = -7/13 . (2/11 + 9/11) + -6/13`
` = -7/13 . 1 + -6/13 = -7/13 + -6/13 = -1`
c, `-5/16 : 0,125 - (2 1/4 - 0,6) . 10/11`
`= - 5/16 . 8 - (9/4 - 3/5) . 10/11`
`= - 5/2 -(45/20 - 12/20). 10/11`
`= -5/2 - 33/20 . 10/11`
`= -5/2 -3/2`
`= -8/2 = -4`
Bài 2:
a, `8/7 x - 1/7 x =2/3`
`x . (8/7 - 1/7) = 2/3`
`x . 1 = 2/3`
`x =2/3`
b, `1/4 + 1/3 : | x - 1| = 1`
` 1/3 : | x - 1| = 1 - 1/4 = 3/4`
` | x - 1| = 1/3 : 3/4 =4/9`
⇒\(\left[ \begin{array}{l}x - 1 = 4/9\\x - 1 = -4/9\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 13/9\\x = 5/9\end{array} \right.\)
Vậy `x ∈ { 13/9 ; 5/9}`
c, `4/(1 . 3) + 4/(3 .5) + .............. + 4/(97 . 99) -x -196/99 = 1`
`2 . (2/(1.3) + 2/(3.5) +.............+ 2/(97.99) ) - x - 196/99= 1`
`2 . (1 - 1/3 + 1/3 - 1/5 + ............. + 1/97 - 1/99) - x - 196/199 = 1`
`2 . (1 - 1/99) - x - 196/99 = 1`
` 2. 98/99 - x -196/99 = 1`
`196/99 - x - 196/99 = 1`
`(196/99 - 196/99) - x = 1`
`-x = 1`
`⇒ x = -1`
