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Đáp án `+` Giải thích các bước giải:

4.

`3 . 5^2 + 15 . 2^2 - 26 : 2`

`= 3 . 25 + 15 . 4 - 13`

`= 75 + 60 - 13`

`= 135 - 13`

`= 122.`

``

`2021 + 5[300 - (17 - 7)^2]`

`= 2021 + 5[300 - 100]`

`= 2021 + 5 . 200`

`= 2021 + 1000`

`= 3021.`

``

`3^2 . 5 + 2^3 . 10 - 81 : 3`

`= 9 . 5 + 8 . 10 - 27`

`= 45 + 80 - 27`

`= 125 - 27`

`= 98.`

``

(5^19 : 5^17 + 3) : 7

= (25 + 3) : 7

= 28 : 7

= 4.

``

`(128 - 97 + 34) - (34 - 97 + 228) - 2021^0`

`= 128 - 97 + 34 - 34 + 97 - 228 - 1`

`= (128 - 228) + (-97 + 97) + (34 - 34) - 1`

`= -100 + 0 + 0 - 1`

`= -100 - 1`

`= -101.`

``

`128 . 46 + 128 . 32 + 128 . 22`

`= 128 . (46 + 32 + 22)`

`= 128 . 100`

`= 12800.`

5.

`165 : x = 3`

`x = 165 : 3`

`x = 55.`

``

`x - 71 = 129`

`x = 129 + 71`

`x = 200.`

``

`9^(x - 1) = 9`

`9^(x - 1) = 9^1`

`x - 1 = 1`

`x = 1 + 1`

`x = 2.`

``

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

`9(x + 4) - 25 = 5 . 4`

`9(x + 4) - 25 = 20`

`9(x + 4) = 20 + 25`

`9(x + 4) = 45`

`x + 4 = 45 : 9`

`x + 4 = 5`

`x = 5 - 4`

`x = 1.`

``

`135 - 5(x + 4) = 35`

`5(x + 4) = 135 - 35`

`5(x + 4) = 100`

`x + 4 = 100 : 5`

`x + 4 = 20`

`x = 20 - 4`

`x = 16.`

``

`x^4 = 16`

`x^4 = 2^4`

`=> x = 2.`