Bài 3 (2đ): Tìm x biết: a. (x – 8 )( x3+ 8) = 0 b. (4x – 3) – ( x + 5) = 3(10 – x) 10/08/2021 Bởi Maya Bài 3 (2đ): Tìm x biết: a. (x – 8 )( x3+ 8) = 0 b. (4x – 3) – ( x + 5) = 3(10 – x)
Đáp án:+Giải thích các bước giải: `a)(x-8)(x^3+8)=0` `<=>`\(\left[ \begin{array}{l}x-8=0\\x^3+8=0\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=8\\x^3=-8\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=8\\x=-2\end{array} \right.\) `b)(4x-3)-(x+5)=3(10-x)` `<=>4x-3-x-5=30-3x` `<=>4x-x+3x=30+5+3` `<=>6x=38` `<=>x=19/3` Bình luận
a) (x – 8) (x³ + 8) = 0 ⇔ \(\left[ \begin{array}{l}x-8=0\\x³+ 8=0\end{array} \right.\) ⇔ \(\left[ \begin{array}{l}x=8\\x³=-8\end{array} \right.\) ⇔ \(\left[ \begin{array}{l}x=8\\x³=(-2)³\end{array} \right.\) ⇔ ⇔ \(\left[ \begin{array}{l}x=8\\x=-2\end{array} \right.\) Vậy x ∈ {8 ; -2} b) (4x – 3) – ( x + 5) = 3(10 – x) ⇔ 4x – 3 – x – 5 = 30 – 3x ⇔ (4x – x) – (3 +5) – 30 + 3x = 0 ⇔ 3x – 8 – 30 + 3x = 0 ⇔ 6x – 38 = 0 ⇔ 6x = 38 ⇔ x = $\frac{38}{6}$ ⇔ x = $\frac{19}{3}$ Vậy x = $\frac{19}{3}$ Bình luận
Đáp án:+Giải thích các bước giải:
`a)(x-8)(x^3+8)=0`
`<=>`\(\left[ \begin{array}{l}x-8=0\\x^3+8=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=8\\x^3=-8\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=8\\x=-2\end{array} \right.\)
`b)(4x-3)-(x+5)=3(10-x)`
`<=>4x-3-x-5=30-3x`
`<=>4x-x+3x=30+5+3`
`<=>6x=38`
`<=>x=19/3`
a) (x – 8) (x³ + 8) = 0
⇔ \(\left[ \begin{array}{l}x-8=0\\x³+ 8=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=8\\x³=-8\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=8\\x³=(-2)³\end{array} \right.\)
⇔ ⇔ \(\left[ \begin{array}{l}x=8\\x=-2\end{array} \right.\)
Vậy x ∈ {8 ; -2}
b) (4x – 3) – ( x + 5) = 3(10 – x)
⇔ 4x – 3 – x – 5 = 30 – 3x
⇔ (4x – x) – (3 +5) – 30 + 3x = 0
⇔ 3x – 8 – 30 + 3x = 0
⇔ 6x – 38 = 0
⇔ 6x = 38
⇔ x = $\frac{38}{6}$
⇔ x = $\frac{19}{3}$
Vậy x = $\frac{19}{3}$