Tìm x a) 4x.(5x+2) – (10x-3).(2x+7) = 133 b) 3.(6x-5).(4x+1) – (8x+3).(9x-2) = 203

$a$) ` 4x.(5x+2) – (10x-3).(2x+7) = 133`

`⇔ 20x^2 + 8x – (20x^2 – 6x + 70x – 21) = 133`

`⇔ 20x^2 + 8x – 20x^2 + 6x – 70x + 21 = 133`

`⇔ -56x =112`

`⇔ x = -2`

  Vậy `x=-2`

$b$) `3.(6x-5).(4x+1) – (8x+3).(9x-2) = 203`

`⇔ (18x-15).(4x+1) – (72x^2 + 27x – 16x – 6) = 203`

`⇔ (72x^2 – 60x + 18x – 15) – 72x^2- 27x + 16x + 6= 203`

`⇔ -53x= 212`

`⇔ x = -4`

  Vậy `x=-4`.