a) (x+1)(x2−x+1)=x3−x2+x+x2−x+1=x3−1
b) (x3+x2+x+1)(x−1)=x4−x3+x3−x2+x2−x+x−1=x4−1;
c) (x+a)(x+b)=x2+bx+ax+ab=x2+9b+a)x+ab=x2+(a+b)x+ab
