If the above equation is reduced to zero, this implies that the given power series is a solution to the given differential equation. Now, is to make the summation index and the power of
for the three series, in the same phase. We, first, have to assure that the first terms, for the three-power series, are raised to the same power, which is the case. Now, we do the shift by replacing the summation index, for the third power series, by
instead of n. Note that, this wouldn't affect the terms of the series, The shift yields the same terms.
For the first series, we let
The summation becomes:![]()
Thus, the given power series is the solution of the given differential equation.