Rút gọn biểu thức.
a) \(\frac{1}{2}x\left(1+2x\right)+\left(1-x\right)\left(x+2\right)\)
b) \(\left(2x-1\right)^3-\left(3+2x\right)\left(2x-3\right)+8x^2\left(2-x\right)\)
c) \(x\left(x-1\right)\left(x+1\right)-\left(x+1\right)\left(x^2-x+1\right)\)