(x-(i-1))*(x-(i+1))
(x−(i−1))∗(x−(i+1))=[(x−i)+1][(x−i)−1]=(x−i)2−1 =x2−2xi+i2−1|i2=−1 =x2−2xi−2=(x2−2)−2xi
(x−(i−1))∗(x−(i+1))=x2−x(i+1)−x(i−1)+(i2−1)=x2−xi−x−xi+x+(−1−1)=x2−2xi−2=x2−2−2xi
