` b) 4x -5+2.(2x -3.(x-4) =27` `c) 2x.(x² +x-8) -(x+3).(2x-1) =3.(1-x)` 02/07/2021 Bởi Brielle ` b) 4x -5+2.(2x -3.(x-4) =27` `c) 2x.(x² +x-8) -(x+3).(2x-1) =3.(1-x)`
Đáp án: `b)4x-5+2(2x-3)(x-4)=27` `<=>4x-5+2(2x^2-11x+12)=27` `<=>4x-5+4x^2-22x+24=27` `<=>4x^2-18x+19=27` `<=>4x^2-18x-8=0` `<=>2x^2-9x-4=0` `Delta=81+2.4.4=113` `=>` \(\left[ \begin{array}{l}x_1=\dfrac{9+\sqrt{113}}{4}\\x_2=\dfrac{9-\sqrt{113}}{4}\end{array} \right.\) `c)2x(x^2+x-8)-(x+3)(2x-1)=3(1-x)` `<=>2x^3+2x^2-16x-2x^2-5x+3=3-3x` `<=>2x^3-21x+3=3-3x` `<=>2x^3-18x=0` `<=>x^3-9x=0` `<=>x(x^2-9)=0` `<=>x(x-3)(x+3)=0` `<=>` \(\left[ \begin{array}{l}x=0\\x=3\\x=-3\end{array} \right.\) Bình luận
`b) 4x -5+2.(2x -3.(x-4) )=27` `⇔4x -5 +2.(2x -3x +12) =27` `⇔4x -5 +2.(-x+12) =27` `⇔4x -5 -2x +24 =27` `⇔2x +19 =27` `⇔2x =8` `⇔x =4` `c)2x.(x² +x-8) -(x+3).(2x-1) =3.(1-x)` `⇔2x³ +2x² -16x -(2x² +5x -3) =3 -3x` `⇔2x³ +2x² -16x -2x² -5x +3 -3+3x=0` `⇔2x³ -18x =0` `⇔2x.(x²-9)=0` `<=>` \(\left[ \begin{array}{l}2x = 0\\x^2 – 9 = 0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=0\\x=±3\end{array} \right.\) Bình luận
Đáp án:
`b)4x-5+2(2x-3)(x-4)=27`
`<=>4x-5+2(2x^2-11x+12)=27`
`<=>4x-5+4x^2-22x+24=27`
`<=>4x^2-18x+19=27`
`<=>4x^2-18x-8=0`
`<=>2x^2-9x-4=0`
`Delta=81+2.4.4=113`
`=>` \(\left[ \begin{array}{l}x_1=\dfrac{9+\sqrt{113}}{4}\\x_2=\dfrac{9-\sqrt{113}}{4}\end{array} \right.\)
`c)2x(x^2+x-8)-(x+3)(2x-1)=3(1-x)`
`<=>2x^3+2x^2-16x-2x^2-5x+3=3-3x`
`<=>2x^3-21x+3=3-3x`
`<=>2x^3-18x=0`
`<=>x^3-9x=0`
`<=>x(x^2-9)=0`
`<=>x(x-3)(x+3)=0`
`<=>` \(\left[ \begin{array}{l}x=0\\x=3\\x=-3\end{array} \right.\)
`b) 4x -5+2.(2x -3.(x-4) )=27`
`⇔4x -5 +2.(2x -3x +12) =27`
`⇔4x -5 +2.(-x+12) =27`
`⇔4x -5 -2x +24 =27`
`⇔2x +19 =27`
`⇔2x =8`
`⇔x =4`
`c)2x.(x² +x-8) -(x+3).(2x-1) =3.(1-x)`
`⇔2x³ +2x² -16x -(2x² +5x -3) =3 -3x`
`⇔2x³ +2x² -16x -2x² -5x +3 -3+3x=0`
`⇔2x³ -18x =0`
`⇔2x.(x²-9)=0`
`<=>` \(\left[ \begin{array}{l}2x = 0\\x^2 – 9 = 0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=0\\x=±3\end{array} \right.\)