Tìm x a) 4x.(5x+2) – (10x-3).(2x+7) = 133 b) 3.(6x-5).(4x+1) – (8x+3).(9x-2) = 203 03/08/2021 Bởi Valerie 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`. Bình luận
$a$) ` 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`.
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