(1)(x?1)(x+1)=x2?1,
故答案为:x2?1;
(2)(x?1)(x2+x+1)=x3+x2+x?x2?x?1=x3?1,
故答案为:x3?1;
(3)(x?1)(x3+x2+x+1)=x4+x3+x2+x?x3?x2?x?1=x4?1,
(x?1)(x99+x98+…+x+1)=x100?1,
故答案为:x4?1,x100?1;
(1)299+298+…+2+1=(2?1)(299+298+…+2+1)=2100?1;
(2)(?3)50+(?3)49+…+(?3)+1=?14(?3?1)[)(?3)50+(?3)49+…+(?3)+1]=?14[(?3)51?1]=3514+14