Đáp án:
$a)5(x+y-2z)(x+y+2z)\\ b)(x+2)(x+y-2)\\ c)(x-5)(x-6)(x-4)\\ d)2(x+1-y)(x+1+y).$
Giải thích các bước giải:
$a)5x^2+10xy+5y^2-20z^2\\ =5(x^2+2xy+y^2-4z^2)\\ =5\left(x+y)^2-(2z)^2\right)\\ =5(x+y-2z)(x+y+2z)\\ b)x^2+2xy+y^2-2x-2y\\ =(x+y)^2-2(x+y)\\ =(x+2)(x+y-2)\\ c)(x-5)^3-x+5\\ =(x-5)^3-(x-5)\\ =(x-5)((x-5)^2-1)\\ =(x-5)(x-5-1)(x-5+1)\\=(x-5)(x-6)(x-4)\\ d)2x^2+4x+2-2y^2\\ =2(x^2+2x+1-y^2)\\ =2\left((x+1)^2-y^2\right)\\ =2(x+1-y)(x+1+y).$
