`4/5 xx 3/7 + 4/5 xx 6/7 - 4/5 xx 4/14`

`= 4/5 xx (3/7 + 6/7 - 2/7)`

`= 4/5 xx 1`

`= 4/5`

`(4 xx 5 xx 6)/(3 xx 8 xx 10)`

`= (2 xx 2 xx 5 xx 3 xx 2)/(3 xx 2 xx 4 xx 2 xx 5)`

`= (cancel{2} xx cancel{2} xx cancel{5} xx cancel{3} xx 2)/(cancel{3} xx cancel{2} xx 4 xx cancel{2} xx cancel{5})`

`= 2/4 = 1/2`

`1/2x + 3/4 = -3/10`

`1/2x = -3/10 - 3/4`

`1/2x = -21/20`

`=> x = -21/10`

Vậy `x = -21/10`

Làm vô câu của tớ ik

`D(x) = (x + 1)(2x - 7)`

`(x + 1)(2x - 7) = 0`

`<=>` $\left[\begin{matrix} x + 1 = 0\\ 2x - 7 = 0\end{matrix}\right.$

`<=>` $\left[\begin{matrix} x = -1\\ x = 7/2\end{matrix}\right.$

Vậy .......