Hoặc
Tính các tổng sau:
x2−2x(x−1)2+2−xx(x−1)2;
x2−2x(x−1)2+2−xx(x−1)2
=x2−2+2−xx(x−1)2=x2−xx(x−1)2
=x(x−1)x(x−1)2=1x−1.