Tìm x a) (8x-3) . (3x+2) – (4x+7) . (x+4) = (2x+1) . (5x-1) b) (3x −5)(7 −5x) − (5x + 2)(2 −3x) = 4 14/07/2021 Bởi Genesis Tìm x a) (8x-3) . (3x+2) – (4x+7) . (x+4) = (2x+1) . (5x-1) b) (3x −5)(7 −5x) − (5x + 2)(2 −3x) = 4
`a,` `(8x-3)(3x+2)-(4x+7)(x+4) = (2x+1)(5x-1)` `⇒ 20x^2 – 16x – 34 = 10x^2 + 3x – 1` `⇒ 20x^2 – 16x – 33 = 10x^2 + 3x` `⇒ 20x^2 – 19x – 33 = 10x^2` `⇒ 10x^2 – 19x – 33 = 0` `⇒ (x-3)(10x+11) = 0` `⇒`\(\left[ \begin{array}{l}x-3=0\\10x+11=0\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}x=3\\x=-\dfrac{11}{10}\end{array} \right.\) Vậy `x = 3 , x = -11/10` `b,` `(3x-5)(7-5x) – (5x+2)(2-3x) = 4` `⇒ -15x^2 + 46x – 35 – (5x+2)(2-3x) = 4` `⇒ -15x^2 + 46x – 35 + 15x^2 – 4x – 4 = 4` `⇒ 42x – 39 = 4` `⇒ 42x = 4 + 39` `⇒ 42x = 43` `⇒ x = 43/42` Vậy `x = 43/42` Bình luận
Đáp án+Giải thích các bước giải: `a)` `(8x-3).(3x+2)-(4x+7).(x+4)=(2x+1).(5x-1)` `<=>24x^2+16x-9x-6-(4x^2+16x+7x+28)=10x^2-2x+5x-1` `<=>24x^2+16x-9x-6-4x^2-16x-7x-28=10x^2-2x+5x-1` `<=>20x^2-16x-34=10x^2+3x-1` `<=>10x^2-19x-33=0` `<=>10x^2-30x+11x-33=0` `<=>10x.(x-3)+11.(x-3)=0` `<=>(10x+11).(x-3)=0` `<=>`\(\left[ \begin{array}{l}10x+11=0\\x-3=0\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=\dfrac{-11}{10}\\x=3\end{array} \right.\) Vậy `x=3` hoặc `x=-11/10` là giá trị cần tìm. `b)` `(3x-5).(7-5x)-(5x+2).(2-3x)=4` `<=>21x-15x^2-35+25x-(10x-15x^2+4-6x)=4` `<=>21x-15x^2-35+25x-10x+15x^2-4+6x=4` `<=>42x=4+35+4` `<=>42x=43` `<=>x=(43)/(42)` Vậy `x=(43)/(42)` là giá trị cần tìm. Bình luận
`a,`
`(8x-3)(3x+2)-(4x+7)(x+4) = (2x+1)(5x-1)`
`⇒ 20x^2 – 16x – 34 = 10x^2 + 3x – 1`
`⇒ 20x^2 – 16x – 33 = 10x^2 + 3x`
`⇒ 20x^2 – 19x – 33 = 10x^2`
`⇒ 10x^2 – 19x – 33 = 0`
`⇒ (x-3)(10x+11) = 0`
`⇒`\(\left[ \begin{array}{l}x-3=0\\10x+11=0\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=3\\x=-\dfrac{11}{10}\end{array} \right.\)
Vậy `x = 3 , x = -11/10`
`b,`
`(3x-5)(7-5x) – (5x+2)(2-3x) = 4`
`⇒ -15x^2 + 46x – 35 – (5x+2)(2-3x) = 4`
`⇒ -15x^2 + 46x – 35 + 15x^2 – 4x – 4 = 4`
`⇒ 42x – 39 = 4`
`⇒ 42x = 4 + 39`
`⇒ 42x = 43`
`⇒ x = 43/42`
Vậy `x = 43/42`
Đáp án+Giải thích các bước giải:
`a)`
`(8x-3).(3x+2)-(4x+7).(x+4)=(2x+1).(5x-1)`
`<=>24x^2+16x-9x-6-(4x^2+16x+7x+28)=10x^2-2x+5x-1`
`<=>24x^2+16x-9x-6-4x^2-16x-7x-28=10x^2-2x+5x-1`
`<=>20x^2-16x-34=10x^2+3x-1`
`<=>10x^2-19x-33=0`
`<=>10x^2-30x+11x-33=0`
`<=>10x.(x-3)+11.(x-3)=0`
`<=>(10x+11).(x-3)=0`
`<=>`\(\left[ \begin{array}{l}10x+11=0\\x-3=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{-11}{10}\\x=3\end{array} \right.\)
Vậy `x=3` hoặc `x=-11/10` là giá trị cần tìm.
`b)`
`(3x-5).(7-5x)-(5x+2).(2-3x)=4`
`<=>21x-15x^2-35+25x-(10x-15x^2+4-6x)=4`
`<=>21x-15x^2-35+25x-10x+15x^2-4+6x=4`
`<=>42x=4+35+4`
`<=>42x=43`
`<=>x=(43)/(42)`
Vậy `x=(43)/(42)` là giá trị cần tìm.