Bài 1. Tìm x :
1/ ( 2x – 5 ) + 17 = 6.
2/ 10 – 2 ( 4 – 3x ) = – 4.
3/ – 12 + 3 ( – x + 7 ) = – 18.
4/ 24 : ( 3x – 2 ) = – 3.
5/ – 45 : 5 . ( – 3 – 2x ) = 3.
Bài 2. Tìm x :
1/ x . ( x + 7 ) = 0
2/ ( x + 12 ) . ( x – 3 ) = 0.
3/ ( – x + 5 ) . ( 3 – x ) = 0.
4/ x . ( 2 + x ) . ( 7 – x ) = 0.
5/ ( x – 1 ) . ( x + 2 ) . ( – x – 3 ) = 0.
Bài 1: Tìm x:
1/ $( 2x – 5 ) + 17 = 6$
⇔ $2x – 5 + 17 = 6$
⇔ $2x + 12 = 6$
⇔ $2x = 6 – 12$
⇔ $2x = -6$
⇔ $x = ( – 6) ÷ 2$
⇔ $x = -3$
2/ $10 – 2( 4 – 3x ) = -4$
⇔ $10 – ( 2.4 – 2.3x ) = -4$
⇔ $10 – 8 + 6x = -4$
⇔ $2 + 6x = -4$
⇔ $6x = -4-2$
⇔ $6x = -6$
⇔ $x = ( -6)÷6$
⇔ $x = -1$
3/ $-12 + 3( -x + 7 ) = -18$
⇔$-12 -3x + 21 = -18$
⇔$9 – 3x = -18$
⇔ $-3x = -18 – 9$
⇔ $-3x = -27$
⇔ $x = 9$
4/ $24 : ( 3x – 2)=-3$
⇔ $3x – 2 = 24÷(-3)$
⇔ $3x – 2 = -8$
⇔ $3x = -8 + 2$
⇔ $3x = -6$
⇔ $x = -2$
5/ $-45 ÷ 5 . ( -3 – 2x ) = 3$
⇔ $27 + 18x = 3$
⇔ $18x = -24$
⇔ $x = \dfrac{-24}{18}$
Bài 2: Tìm x
1/ $x .(x+7)=0$
⇔ \(\left[ \begin{array}{l}x=0\\x+7=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=0\\x=-7\end{array} \right.\)
2/ $( x + 12 ). ( x – 3) = 0$
⇔ $\(\left[ \begin{array}{l}x+12=0\\x-3=0\end{array} \right.\)$
⇔ $\(\left[ \begin{array}{l}x=-12\\x=3\end{array} \right.\)$
3/ $( -x + 5 ) .(3-x) = 0$
⇔ \(\left[ \begin{array}{l}-x+5=0\\3-x=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=5\\x=3\end{array} \right.\)
4/ $x(2+x)(7-x)=0$
⇔ $x = 0;$ $2+x=0$ và $7-x=0$
⇔ $x = 0$ ; $x = -2$ và $x = 7$
5/ $( x -1)(x+2)(-x-3)=0$
⇔ $x -1 = 0$; $x+2=0$ và $-x-3=0$
⇔ $x = 1$; $x =-2$ và $x = -3$
Đáp án:
Bài `1`
` 1)`
` (2x -5) + 17 = 6 `
` 2x -5 +17= 6`
` 2x +12 = 6`
` 2x= -6`
` x =-3`
`2)`
` 10 – 2(4-3x) = -4`
` 10 – 8 + 6x + 4 = 0`
` 6x + 6 = 0`
` 6x = -6`
` x= -1`
`3)`
` -12 + 3(-x+7) = -18`
` 3(-x+7) = -6`
` – x +7 = -2`
` -x = -9`
`
` x = 9`
`4)`
` 24 : (3x-2) = -3`
` 3x -2 = -8`
` 3x = -6`
` x = -2`
`5)`
` -45 : 5(-3 -2x) = 3`
` 5(-3x-2) = -15`
` -3x -2 = -3`
` -3x = -1`
` x = 1/3`
Bài `2`
` 1)`
` => ` \(\left[ \begin{array}{l}x=0\\x+7=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=0\\x=-7\end{array} \right.\)
`2)`
` => ` \(\left[ \begin{array}{l}x+12=0\\x-3=0\end{array} \right.\)
` =>` \(\left[ \begin{array}{l}x=-12\\x=3\end{array} \right.\)
`3)`
` => ` \(\left[ \begin{array}{l}-x+5=0\\3-x=0\end{array} \right.\)
` =>` \(\left[ \begin{array}{l}x=5\\x=3\end{array} \right.\)
`4)`
` => x = 0`
hoặc ` 2 + x = 0` hoặc ` 7 – x = 0`
` => x = 0` hoặc ` x = -2 ; x =7`
`5)`
` => x -1 = 0` hoặc ` x +2 = 0` hoặc ` -x-3 = 0`
` => x =1` ; ` x = -2 ; x = 3`