1. **Assume a power series solution:**
y(x) = \sum_{n=0}^{\infty} a_n x^n
2. **Find the derivatives of \( y(x) \):**
y'(x) = \sum_{n=1}^{\infty} a_n n x^{n-1}
y''(x) = \sum_{n=2}^{\infty} a_n n (n-1) x^{n-2}
3. **Substitute the series and its derivatives into the differential equation:**
\sum_{n=2}^{\infty} a_n n (n-1) x^{n-2} - 4 \sum_{n=1}^{\infty} a_n n x^{n-1} + \sum_{n=0}^{\infty} a_n e^x x^n = x^2
4. **Equate the series on both sides of the equation:**
- Matching coefficients for \( x^0 \):
a_0 = 1
- Matching coefficients for \( x^1 \):
a_1 = 1
- Matching coefficients for \( x^2 \):
2a_2 - 4a_1 = 0 \implies a_2 = 2
- Matching coefficients for \( x^3 \):
6a_3 - 4a_2 = 0 \implies a_3 = \frac{4}{3}
- Matching coefficients for \( x^4 \):
12a_4 - 8a_3 + a_0 = 1 \implies 12a_4 - 8 \left( \frac{4}{3} \right) + 1 = 1 \implies a_4 = \frac{5}{12}
5. **Combine the coefficients to write the power series solution:**
y(x) = 1 + x + 2 x^2 + \frac{4}{3} x^3 + \frac{5}{12} x^4
Therefore, the solution up to and including the term involving \( x^4 \) is:
y(x) = 1 + x + \frac{x^2}{2} + \frac{x^3}{6} + \frac{5x^4}{24}