Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 326 / 3 / 1 / d / Solution

Comparison with zero and nonnegativity of the two terms givesThereforeFor a concrete variational regularization example, take a Hilbert space and $J(u)=\Vert u{\Vert }^2$. The bound forces $u_{\alpha }\to 0$ in norm. Since $K$ is a bounded linear operator, $K{u}_{\alpha }\to 0$, and continuity of the squared norm givesThe same conclusion is not forced by $J(u_{\alpha })\to 0$ for a regulariser with a nontrivial zero set.