Question

Answer 1

`a,` `(x-2)(x^2 + 2x +4)`

`= x^3 + 2x^2 + 4x - 2x^2 - 4x - 8`

`= x^3 + (2x^2 - 2x^2) + (4x-4x) - 8`

`= x^3 - 8`

Với `x = 3`

`=>  3^3 - 8 = 27 - 8 = 19`

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`b,` `(x+1)(x^7 - x^6 + x^5 - x^4 + x^3 -x^2 + x - 1)`

`= x^8 - x^7 + x^6 - x^5 + x^4 - x^3 + x^2 - x + x^7 - x^6 + x^5 - x^4 + x^3 -x^2 + x - 1`

`= x^8 + (-x^7 + x^7) + (x^6 - x^6) + (-x^5 + x^5) + (x^4 - x^4) + (-x^3 + x^3) + (x^2 - x^2) + (x-x) -1`

`= x^8 - 1`

Với `x=2`

`=> 2^8 - 1 = 256 -1=255`