3.1-2

[songjiyang]

Why the "a" in the following polynomial is ignored?

[songjiyang]

[uuanqin]

I think you are right.

[gaogzhen]

I also don't understand how it can put $C_0^ba^0+C_1^ba^1 + \cdots+C_b^ba^B$ reduce to $C_0^b+C_1^b+\cdots C_b^b$. I think layer master's answer is right.

[newptcai]

This proof is still incorrect as the question does not assume $b$ is an integer. Thus we can not apply binomial theorem here.