Which of the following expresses ridge regression as a constrained optimization problem?

• A. Minimizes the sum of squared residuals with an L1 penalty on the coefficients.
• B. Minimizes the sum of squared residuals with an L2 penalty on the coefficients.
• C. Minimizes the sum of squared residuals subject to the sum of squares of the coefficients being at most a value.
• D. Maximizes the likelihood with an L2 penalty.

Answer: (C)