Đáp án:
$1)A=211\\ 2)B=255\\ 3)C=127\\ 4)D=-5$
Giải thích các bước giải:
$1)\\ A=(x-2)(x^4+2x^3+4x^2+8x+16)\\ =x^5+2x^4+4x^3+8x^2+16x-2x^4-4x^3-8x^2-16x-32\\ =x^5-32\\ A=3 \Rightarrow A=3^5-32=211\\ 2)\\ B=(x+1)(x^7-x^6+x^5-x^4+x^3-x^2+x-1)\\ =x^8-x^7+x^6-x^5+x^4-x^3+x^2-x+x^7-x^6+x^5-x^4+x^3-x^2+x-1\\ =x^8-1\\ x=2 \Rightarrow B=2^8-1=255\\ 3)\\ C=(x+1)(x^6-x^5+x^4-x^3+x^2-x+1)\\ =x^7-x^6+x^5-x^4+x^3-x^2+x+x^6-x^5+x^4-x^3+x^2-x+1\\ =x^7+1\\ x=2 \Rightarrow B=2^7-1=127\\ 4)\\ D=2x(10x^2-5x-2)-5x(4x^2-2x-1)\\ =20x^3-10x^2-4x-20x^3+10x+5x\\ =x\\ x=-5 \Rightarrow D=-5$
