Bài 6. Tìm x biết a. 89 – (73 – x) = 20 b. (x + 7) – 25 = 13 c. 98 – (x + 4) = 20 d. 140 : (x – 8) = 7 e. 4(x + 41) = 400 f. x – [ 42 + (–28)] = –8 g. x + 5 = 20 – (12 – 7) h. (x – 11) = 2.2³ + 20 : 5 i. 4(x – 3) = 7² – 1³. j. 2x+1.22014 = 22015. k. 2x – 49 = 5.3² ℓ. 3²(x + 14) – 5² = 5.2² m. 6x + x = 511 : 59 + 31. n. 7x – x = 521 : 519 + 3.2² – 70. o. 7x – 2x = 617 : 615 + 44 : 11. p. 3x = 9 q. 4x = 64 r. 9x–1 = 9 s. x4 = 16 t. 2x : 25 = 1

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Giải thích các bước giải:

`B_6.`

`a)` `89 - (73 - x) = 20`

`=> 73 - x = 89 - 20`

`=> 73 - x = 69`

`=> x = 73 - 69`

`=> x = 4`

Vậy `x = 4`

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`b)` `(x + 7) - 25 = 13`

`=>x + 7 = 13 + 25`

`=> x + 7 = 38`

`=> x = 38 - 7`

`=> x = 31`

Vậy `x = 31`

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`c)` `98 - (x + 4) = 20`

`=> x + 4 = 98 - 20`

`=> x + 4 = 78`

`=> x = 78 - 4`

`=> x = 74`

Vậy `x = 74`

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`d)` `140: (x - 8) = 7`

`=> x - 8 = 140 : 7`

`=> x - 8 = 20`

`=> x = 20 + 8`

`=> x = 28`

Vậy `x = 28`

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`e)` `4 xx (x + 41) = 400`

`=> x + 41 = 400 : 4`

`=> x + 41 = 100`

`=> x = 100 - 41`

`=> x = 59`

Vậy `x = 59`

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`f)` `x - [42 + (-28)] = - 8`

`=> x - 14 = -8`

`=> x = -8 + 14`

`=> x = 6`

Vậy `x = 6`

---------------

`g)` `x + 5 = 20 - (12 - 7)`

`=> x + 5 = 20 - 5`

`=>x + 5 = 15`

`=> x = 15 - 5`

`=> x = 10`

Vậy `x = 10`

---------------

`h)` `(x - 11) = 2 . 2^3 + 20 : 5`

`=> x - 11 = 2 xx 8 + 4`

`=> x - 11 = 16 + 4`

`=> x - 11 = 20`

`=> x = 20 + 11`

`=> x = 31`

Vậy `x = 31`

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`i)` `4 xx (x - 3) = 7^2 - 1^3`

`=> 4 xx (x - 3) = 49 - 1`

`=> 4 xx (x - 3) = 48`

`=> x - 3 = 48 : 4`

`=> x - 3 = 12`

`=> x = 12 + 3`

`=> x = 15`

Vậy `x = 15` 

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Sửa đề: `j)` `2x + 1 xx 2^2014 = 2^2015`

`=> 2x + 1 = 2^2015 : 2^2014`

`=> 2x + 1 = 2`

`=> 2x = 2 - 1`

`=> 2x = 1`

`=> x = 1 : 2`

`=> x = 1/2`

Vậy `x = 1/2`

-----------------

`k)` `2x - 49 = 5 xx 3^2`

`=> 2x - 49 = 5 xx 9`

`=> 2x - 49 = 45`

`=> 2x = 45 + 49`

`=> 2x = 94`

`=> x = 94 : 2`

`=> x =47`

Vậy `x = 47`

-----------------

`l)` `3^2 xx (x + 14) - 5^2 = 5 xx 2^2`

`=> 9 xx (x + 14) - 25 = 5 xx 4`

`=> 9 xx (x + 14) - 25 = 20`

`=> 9 xx (x + 14) = 20 + 25`

`=> 9 xx (x + 14) = 45`

`=> x + 14 = 45 : 9`

`=> x + 14 = 5`

`=> x = 5 - 14`

`=> x = -9`

Vậy `x = -9`

-----------------

Sửa đề: `m)` `6x + x = 5^11 : 5^9 + 31`

`=> 7x = 5^2 + 31`

`=> 7x = 25 + 31`

`=> 7x = 56`

`=> x = 8`

Vậy `x = 8`

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Sửa đề: `n) 7x - x = 5^21 : 5^19 + 3 xx 2^2 - 70`

`=> 6x = 5^2 + 3 xx 4 - 70`

`=> 6x = 25 + 12 - 70`

`=> 6x = -33`

`=> x = -33/6`

Vậy `x = -33/6`

------------------

Sửa đề: `o)` `7x - 2x = 6^17 : 6^15 + 44 : 11`

`=>5x = 6^2 + 4`

`=> 5x = 36 + 4`

`=> 5x = 40`

`=> x = 40 : 5`

`=> x = 8`

Vậy `x = 8`

-------------------

`p)` `3x = 9`

`=> x = 9 : 3`

`=> x = 3`

Vậy `x = 3`

--------------------

`q)` `4x = 64`

`=> x = 64 : 4`

`=> x = 16`

Vậy `x = 16`

--------------------

`r)` `9x - 1 = 9`

`=> 9x = 9 + 1`

`=> 9x = 10`

`=> x = 10/9`

Vậy `x = 10/9`