ANSWER
The radius is 4
EXPLANATION
The given equation is:

We complete the square to get the expression in standard form:


We factor using perfect squares to get:

This implies that,

Comparing to

The radius is r=4
To find the length I know you have to do 164 divided by 6
I think it going to be 21/2 or 10 1/2
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

