giúp tớ plss

Bài 4: 1) $~(x+1)^3-(x-4)(x+4)-x^3$ $= (x^3 + 3x^2 + 3x + 1) - (x^2 - 16) - x^3$ $= x^3 + 3x^2 + 3x + 1 - x^2 + 16 - x^3$ $= 3x^2 + 3x + 17$ 2) $~(x+2)^3-x(x+3)(x-3)-12x^2-8$ $= (x^3 + 6x^2 + 12x + 8) - (x^2 - 9x) - 12x^2 - 8$ $= x^3 + 6x^2 + 12x + 8 - x^2 + 9x - 12x^2 - 8$ $= -5x^2 + 21x$ 3) $~(x-2)^3-x(x-2)(x+2)+6x(x-3)$ $= (x^3 - 6x^2 + 12x - 8) - (x^3 - 4x) + 6x^2 - 18x$ $= x^3 - 6x^2 + 12x - 8 - x^3 + 4x + 6x^2 - 18x$ $= -8$ 4) $~x(x-5)(x+5)-(x-5)^3+100x$ $= (x^3 - 25x) - (x^3 - 15x^2 + 75x - 125) + 100x$ $= x^3 - 25x - x^3 + 15x^2 - 75x + 125 + 100x$ $= 15x^2 - 50x + 125$ 5) $~(x-3y)^3-(x-2y)(2y+x)$ $= (x^3 - 9x^2y + 27xy^2 - 27y^3) - (x^2 - 4y^2)$ $= x^3 - 9x^2y + 27xy^2 - 27y^3 - x^2 + 4y^2$ $= x^3 - 9x^2y + 27xy^2 - 23y^3 - x^2$ 6) $~(-x-2y)^3+x(2y-x)(x+2y)$ $= (-x)^3 - 3(-x)^2(2y) + 3(-x)(2y)^2 - (2y)^3 + x(2y - x)(x + 2y)$ $= -x^3 + 6x^2y - 12xy^2 + 8y^3 + x(4y^2 - x^2)$ $= -x^3 + 6x^2y - 12xy^2 + 8y^3 + 4xy^2 - x^3$ $= -2x^3 + 6x^2y - 8xy^2 + 8y^3$ 7) $~-(2x-y)^3-x(2x-y)^2-y^3$ $= -(8x^3 - 12x^2y + 6xy^2 - y^3) - x(4x^2 - 4xy + y^2) - y^3$ $= -8x^3 + 12x^2y - 6xy^2 + y^3 - 4x^3 + 4x^2y - xy^2 - y^3$ $= -12x^3 + 16x^2y - 7xy^2$ 8) $~-x(x-y)^2+(x-y)^3+y^2(y-2x)$ $= -x(x^2 - 2xy + y^2) + (x^3 - 3x^2y + 3xy^2 - y^3) + y^3 - 2x^2y$ $= -x^3 + 2x^2y - xy^2 + x^3 - 3x^2y + 3xy^2 - y^3 + y^3 - 2x^2y$ $= 0$ Vậy các biểu thức đã cho được rút gọn như sau: 1) $3x^2 + 3x + 17$ 2) $-5x^2 + 21x$ 3) $-8$ 4) $15x^2 - 50x + 125$ 5) $x^3 - 9x^2y + 27xy^2 - 23y^3 - x^2$ 6) $-2x^3 + 6x^2y - 8xy^2 + 8y^3$ 7) $-12x^3 + 16x^2y - 7xy^2$ 8) $0$.