Main Answer:
The formal Fourier series solution of the endpoint value problem involves finding an analytical expression for the solution using Fourier series expansion. Therefore, option a) Analytical expression is the correct choice.
Step-by-step explanation:
a) Analytical expression:
The formal Fourier series solution is derived by expressing the given function as a sum of sines and cosines through Fourier series expansion. This analytical expression provides a closed-form solution using trigonometric functions.
b) Numerical approximation, c) Graphical representation, and d) Closed-form solution may be relevant in different contexts, but for the formal Fourier series solution, the focus is on obtaining an analytical expression through the Fourier series expansion.