Let

Differentiating twice gives


When x = 0, we observe that y(0) = a₀ and y'(0) = a₁ can act as initial conditions.
Substitute these into the given differential equation:


Then the coefficients in the power series solution are governed by the recurrence relation,

Since the n-th coefficient depends on the (n - 2)-th coefficient, we split n into two cases.
• If n is even, then n = 2k for some integer k ≥ 0. Then




It should be easy enough to see that

• If n is odd, then n = 2k + 1 for some k ≥ 0. Then




so that

So, the overall series solution is


Since only the principal value, interest rate and interest period are given, we can deduce that "finance charge" only includes the interest to be paid at the end of the term. This can be obtained by subtracting the principal value from the future value which we will solve for.
The future value can be solved by using the following compound interest formula:
Let:
F = Future value
P = Principal value
r<span> = annual interest rate </span>
n<span> = number of times that interest is compounded per year</span>
t<span> = number of years</span>
F = P(1 + r/n)^nt
Substituting the given values:
F = 4250(1 + 0.1325/12)^(12*2)
F = 5531.54
Subtracting P from F:
Finance charge = 5531.54 - 4250 = 1281.54
Therefore the finance charge is $1,281.54