Rút gọn biểu thức: a,(x-3)^2-(x+1)(x-5) b,(x-1)(x^2+x+1)-(2x+1)(1-2x) c,x^2-2x:(-1/2x)-(x^2-2x+1):(x-1)

a) `(x-3)^2 -(x+1)(x-5) = x^2-6x+9-x^2+4x+5 = -2x+4`

b) `(x-1)(x^2+x+1)-(2x+1)(1-2x) = (x^3-1)-[(2x)^2-1^2]`

`= x^3-1-4x^2+1=x^3-4x^2`

c) `x^2-2x : (-1/2 x) – (x^2-2x+1):(x-1)`

`= x^2 + 4x^2 – (x-1)^2 :(x-1) = 5x^2 – x+1 `