Toán Lớp 6: Tìm x
a) ( -2 ) . ( 4 – 3x ) + 15 = 15 – 2 . (x – 1 )
b) 4 . ( 1 – x ) = 15 – x
c) ( – 2 ) ² . ( x – 8 ) + 2x = 14 – x
d) ( – 2 ) ³ . ( 1 + x ) – 15 = ( -2 ) . ( 3 – x )
e) ( – 3 ) ² + 2 . ( 1 – x ) = 12 – 4 . ( x – 3 )
f ) 15 . ( x + 3 ) – 2 . ( 1 – x ) = 27
g ) 21 . ( x +2 ) – 15 x + 25 = 0
h ) ( – 2 ) ² . ( 1 – x ) = 3 . ( x – 4 )
i ) – ( x + 2 ) + 13 = 15 – 4 . ( 2 + x )
k ) 15 – 3 . ( x – 1 ) = 45 + 3 . ( 2 – x )
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f ) 15 . ( x + 3 ) – 2 . ( 1 – x ) = 27
⇒17x+43=27
⇒17x+43−43=27−43
⇒17x=−16
⇒17x17=−1617
⇒x=−1617
Vậy: x=−1617
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g ) 21 . ( x +2 ) – 15 x + 25 = 0
⇒21(x+2)−15x+25−25=0−25
⇒21(x+2)−15x=−25
⇒6x+42=−25
⇒6x+42−42=−25−42
⇒6x=−67
⇒6x6=−676
⇒x=−676
Vậy: x=−676
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h ) ( – 2 ) ² . ( 1 – x ) = 3 . ( x – 4 )
⇒4−4x=3x−12
⇒4−4x−4=3x−12−4
⇒−4x=3x−16
⇒−4x−3x=3x−16−3x
⇒−7x=−16
⇒−7x−7=−16−7
⇒x=167
Vậy: x=167
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i) −(x+2)+13=15−4(2+x)−(x+2)+13=15−4(2+x)
⇒−x+11=−4x+7
⇒−x+11−11=−4x+7−11
⇒−x=−4x−4
⇒−x+4x=−4x−4+4x
⇒3x=−4
⇒3x3=−43
⇒x=−43
Vậy x=−43
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k) 15−3(x−1)=45+3(2−x)15−3(x−1)=45+3(2−x)
⇒−3x+18=−3x+51
⇒−3x+18−18=−3x+51−18
⇒−3x=−3x+33
⇒−3x+3x=−3x+33+3x
⇒0=33
Vậy không có giá trị x nào.
$a)$ $\left(\:-2\:\right)\:.\:\left(\:4\:-\:3x\:\right)\:+\:15\:=\:15\:-\:2\:.\:\left(x\:-\:1\:\right)$
$⇒\left(-2\right)\left(4-3x\right)+15-15=15-2\left(x-1\right)-15$
⇒$\left(-2\right)\left(4-3x\right)=-2\left(x-1\right)$
$⇒-8+6x=-2x+2$
$⇒-8+6x+8=-2x+2+8$
$⇒6x=-2x+10$
$⇒6x+2x=-2x+10+2x$
$⇒8x=10$
$⇒\dfrac{8x}{8}=\dfrac{10}{8}$
$⇒x=\dfrac{5}{4}$
Vậy $x=\dfrac{5}{4}$
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$b)$ $4\left(1-x\right)=15-x$
$⇒4-4x=15-x$
$⇒4-4x-4=15-x-4$
$⇒-4x=-x+11$
$⇒-4x+x=-x+11+x$
$⇒-3x=11$
$⇒\dfrac{-3x}{-3}=\dfrac{11}{-3}$
$⇒x=-\dfrac{11}{3}$
Vậy $x=-\dfrac{11}{3}$
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$c)$ $\left(-2\right)^2\left(x-8\right)+2x=14-x$
$⇒4\left(x-8\right)+2x=14-x$
$⇒6x-32=14-x$
$⇒6x-32+32=14-x+32$
$⇒6x=-x+46$
$⇒6x+x=-x+46+x$
$⇒7x=46$
$⇒\dfrac{7x}{7}=\dfrac{46}{7}$
$⇒x=\dfrac{46}{7}$
Vậy $x=\dfrac{46}{7}$
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$d)$ $\left(-2\right)^3\left(1+x\right)-15=\left(-2\right)\left(3-x\right)$
$⇒-8\left(1+x\right)-15=\left(-2\right)\left(3-x\right)$
$⇒-8x-23=-6+2x$
$⇒-8x-23+23=-6+2x+23$
$⇒-8x=2x+17$
$⇒-8x-2x=2x+17-2x$
$⇒-10x=17$
$⇒\dfrac{-10x}{-10}=\dfrac{17}{-10}$
$⇒x=-\dfrac{17}{10}$
_______________________________
$e)$ $\left(-3\right)^2+2\left(1-x\right)=12-4\left(x-3\right)$
$⇒9+2\left(1-x\right)=12-4\left(x-3\right)$
$⇒-2x+11=-4x+24$
$⇒-2x+11-11=-4x+24-11$
$⇒-2x=-4x+13$
$⇒-2x+4x=-4x+13+4x$
$⇒2x=13$
$⇒\dfrac{2x}{2}=\frac{13}{2}$
$⇒x=\dfrac{13}{2}$
Vậy $x=\frac{13}{2}$
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$f)$ $15\left(x+3\right)-2\left(1-x\right)=27$
$⇒17x+43=27$
$⇒17x+43-43=27-43$
$⇒17x=-16$
$⇒\dfrac{17x}{17}=\dfrac{-16}{17}$
$⇒x=-\dfrac{16}{17}$
Vậy $x=-\dfrac{16}{17}$
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$g)$ $21\left(x+2\right)-15x+25=0$
$⇒21\left(x+2\right)-15x+25-25=0-25$
$⇒21\left(x+2\right)-15x=-25$
$⇒6x+42=-25$
$⇒6x+42-42=-25-42$
$⇒6x=-67$
$⇒\dfrac{6x}{6}=\dfrac{-67}{6}$
$⇒x=-\dfrac{67}{6}$
Vậy $x=-\dfrac{67}{6}$
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$h)$ $\left(-2\right)^2\left(1-x\right)=3\left(x-4\right)$
$⇒4-4x=3x-12$
$⇒4-4x-4=3x-12-4$
$⇒-4x=3x-16$
$⇒-4x-3x=3x-16-3x$
$⇒-7x=-16$
$⇒\dfrac{-7x}{-7}=\dfrac{-16}{-7}$
$⇒x=\dfrac{16}{7}$
Vậy $x=\dfrac{16}{7}$
_______________________________
$i)$ $-\left(x+2\right)+13=15-4\left(2+x\right)$
$⇒-x+11=-4x+7$
$⇒-x+11-11=-4x+7-11$
$⇒-x=-4x-4$
$⇒-x+4x=-4x-4+4x$
$⇒3x=-4$
$⇒\dfrac{3x}{3}=\dfrac{-4}{3}$
$⇒x=-\dfrac{4}{3}$
Vậy $x=-\dfrac{4}{3}$
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$k)$ $15-3\left(x-1\right)=45+3\left(2-x\right)$
$⇒-3x+18=-3x+51$
$⇒-3x+18-18=-3x+51-18$
$⇒-3x=-3x+33$
$⇒-3x+3x=-3x+33+3x$
$⇒0=33$
Vậy không có giá trị x nào.