`\text{1) x-45=48-68}`

⇒`\text{x-45=-20}`

⇒`\text{x=-20+45}`

⇒`\text{x=25}`

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`\text{2) 35+5.(6-x)=(-12)+112}`

⇒`\text{35+5.(6-x)=100}`

⇒`\text{5.(6-x)=100-35}`

⇒`\text{5.(6-x)=65}`

⇒`\text{6-x=65:5}`

⇒`\text{6-x=13}`

⇒`\text{x=6-13}`

⇒`\text{x=-7}`

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`\text{4) 157-(x-124)=-483}`

⇒`\text{x-124=157-(-483)}`

⇒`\text{x-124=640}`

⇒`\text{x=640+124}`

⇒`\text{x=764}`

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`\text{5) 46-(3x-2)}`$^{2}=(-38)+20$

⇒`\text{46-(3x-2)}`$^{2}=-18$ 

⇒`\text{(3x-2)}`$^{2}=46-(-18)$ 

⇒`\text{(3x-2)}`$^{2}=64$ 

⇒`\text{(3x-2)}`$^{2}=$ $8^{2}$ 

⇒`\text{3x-2=8 hoặc 3x-2=-8}`

⇒`\text{3x=8+2 hoặc 3x=-8+2}`

⇒`\text{3x=10 hoặc 3x=-6}`

⇒$x=\dfrac{10}{3}$ $\text{hoặc x=-2}$

$\text{Mà x thuộc Z (gt)}$⇒$\text{x=-2}$

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$\text{6) 13-(x+6)=-7-10}$

⇒$\text{13-(x+6)=-17}$

⇒$\text{x+6=13-(-17)}$

⇒$\text{x+6=30}$

⇒$\text{x=30-6}$

⇒$\text{x=24}$

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$\text{7) (2x-5)}$$^{3}=$ $15^{2}-4.$ $5^{2}$

⇒$\text{(2x-5)}$$^{3}=225-4.25$ 

⇒$\text{(2x-5)}$$^{3}=225-100$ 

⇒$\text{(2x-5)}$$^{3}=125$ 

⇒$\text{(2x-5)}$$^{3}=$ $5^{3}$ 

⇒$\text{2x-5=5}$

⇒$\text{2x=5+5}$

⇒$\text{2x=10}$

⇒$\text{x=5}$

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$\text{#mct}$

Đáp án:

`1) x = 25`

`2) x = - 7`

`4) x = 764`

`5) x = - 2`

`6) x = 24`

`7) x = 5`

Giải thích các bước giải:

Bài `5 :`

`1) x - 45 = 48 - 68`

`=> x - 45 = - ( 68 - 48 )`

`=> x - 45 = - 20`

`=> x = - 20 + 45`

`=> x = 25`

`2) 35 + 5 . ( 6 - x ) = ( - 12 ) + 112`

`=> 5 . ( 6 - x ) = 112 - 12 - 35`

`=> 5 . ( 6 - x ) = 100 - 35`

`=> 5 . ( 6 - x ) = 65`

`=> 6 - x = 65/5`

`=> 6 - x = 13`

`=> x = 6 - 13 = - 7`

`4) 157 - ( x - 124 ) = - 483`

`=> 157 - x + 124 = - 483`

`=> - x = - 483 - 124 - 157`

`=> - x = - ( 483 + 124 + 157 )`

`=> x = 607 + 157`

`=> x = 764`

`5)` `46 - ( 3x - 2 )^2 = ( - 38 ) + 20`

`=> 46 - ( 3x - 2 )^2 = - 18`

`=> ( 3x - 2 )^2 = 46 + 18`

`=> ( 3x - 2 )^2 = 64`

`=> ( 3x - 2 )^2 ∈ { 8^2 ; ( - 8 )^2 }`

`=> 3x - 2 ∈ { 8 ; - 8 }`

`=> 3x ∈ { 10 ; - 6 }`

`=> x ∈ { 10/3 ; - 2 }`

Mà `x ∈ ZZ => x = - 2`

`6) 13 - ( x + 6 ) = - 7 - 10`

`=> 13 - ( x + 6 ) = - 17`

`=> x + 6 = 13 + 17`

`=> x + 6 = 30`

`=> x = 30 - 6 = 24`

`7)` `( 2x - 5 )^3 = 15^2 - 4 . 5^2`

`=> ( 2x - 5 )^3 = 225 - 4 . 25`

`=> ( 2x - 5 )^3 = 225 - 100`

`=> ( 2x - 5 )^3 = 125`

`=> ( 2x - 5 )^3 = 5^3`

`=> 2x - 5 = 5`

`=> 2x = 10`

`=> x = 10/2 = 5`

Vậy `x = 5`