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The solution of the homogeneous integral equation

\[ x(t) = \lambda \int_{0}^{1} t s\, x(s)\, ds, \]

for \(\lambda \pm 0\), is :

  • A.\(t^{2}\)
  • B.\(1 + t^{2}\)
  • C.\(t\)
  • D.\(1 + t\)

Answer: C

The solution is \(x(t) = t\), up to a constant multiple. (The stem prints '\(\lambda \pm 0\)' where \(\lambda \neq 0\) is meant.)

The kernel \(ts\) is separable. Pulling \(t\) out of the integral:

\[ x(t) = \lambda t \int_{0}^{1} s\, x(s)\, ds = c\,\lambda t \]

so every solution is a multiple of \(t\). Substituting \(x = t\) back gives \(\int_{0}^{1} s^{2}\, ds = 1/3\), so a nonzero solution exists exactly for the eigenvalue \(\lambda = 3\), and the eigenfunction is \(t\).

The forms \(t^{2}\), \(1 + t\) and \(1 + t^{2}\) cannot be solutions, because the right-hand side of the equation is always a multiple of \(t\).

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