\(\dfrac{5}{6}+\dfrac{1}{5}+\dfrac{1}{4}\\ =\dfrac{5\times5\times4}{6\times5\times4}+\dfrac{1\times6\times4}{5\times6\times4}+\dfrac{1\times6\times5}{4\times6\times5}\\ =\dfrac{100}{120}+\dfrac{24}{120}+\dfrac{30}{120}\\ =\dfrac{100+24+30}{120}\\ =\dfrac{154}{120}\\ =\dfrac{77}{60}\)

`b, 11 - (19 - x) = -50`

`19 - x = 11 - (-50)`

`19 - x = 61`

`x = 19 - 61`

`x = -42`

`a, (x - 35) -120 = -6`

`x -35 = -6 + 120`

`x - 35 = 114`

`x = 114 + 35`

`x = 149`

`9. C`

`10. C`

`11. A`

`12. D`

`3 - (x + 1)^2`

`= 3 - (x^2 + 2x + 1)`

`= 3 - x^2 - 2x - 1`

`= 2 - x^2 - 2x`

`1. A`
`2. D`
`3. B`
`5. C`
`6. C`
`7. A`
`8. D`

Để `35 \vdots x,` ta có:

`35 \vdots x` hay `x \in Ư(35) ={+-1;+-5;+-7;+-35}`

Vậy: `x = {+-1;+-5;+-7;+-35}` thì `35\vdots x`