a,\(\frac{\left(2x^3\right)}{4x^7}\)

b,\(\frac{\left(x-1\right)}{\left(x+1\right)^2}.\frac{x^2+2x+1}{x^2-1}\)

c,\(\frac{x^2-7x+12}{x^2-16}\)

d, \(\frac{x-1}{\sqrt{x+1}}:\left(\sqrt{x-1}\right)\)

bài 1:rút gọn biểu thức

a,(2x-5y)(3x-4y)-(x-y)(6x-21y)

b,(x-y)²-(x+y)²

c, (x-1)(x²+3x+1)-x(x²-2)