This eldest brother doesn't seem to understand the proof idea of mathematical induction. Mathematical induction has two steps:

(1) proves that the equation holds when x= initial value;

(2) Assuming that the equation holds when n=k, it is proved that it also holds when n=k+ 1

Note that these two steps are indispensable, because k can be any positive integer, so after n= 1 holds, it can be inferred from the second step that n=2 holds, and then n=3 holds. ...

If the assumption is wrong, your formula is simply wrong, so step one: when x= initial value, the equation does not hold.