Shifting index of summation of power series

dak246
I can't seem to get these power series to match up so that I can solve the equation...heres my work:

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Homework Helper
Looks to me like you went the "wrong direction".

Since the power of x in the first sum is n-2, let j= n-2 so the power becomes xj. If having j in one sum and n in the other bothers you, let j= n in the second sum so it also has xj.