Rút gọn các phân thức :
a, \(\dfrac{x^{2^{ }}-4}{2x^{2^{ }}-4x}\)
b, \(\dfrac{2x-x^2}{x^2-4x+4}\)
c, \(\dfrac{x^2-xy-x+y}{x^2+xy-x-y}\)
d, \(\dfrac{5x^2+10x+5}{x+x^2}\)
e, \(\dfrac{3x^2+3x}{\left(x+1\right) \left(2x+6\right)}\)
f, \(\dfrac{\left(2-3x\right)\left(x+1\right)}{x^2+2x+1}\)