Solution

ID: past-exam-of-the-differential-equations-and-applications-course-of-the-university-of-oxford/2008/a/2/e/solution

The integral equation says precisely with the homogeneous mixed endpoint conditions. Since the supplied satisfies those conditions, apply directly:
No integration is required. The absence of a zero eigenvalue established in (b)–(c) also proves uniqueness of this recovered forcing.

New to topics? Read the docs here!