For each of the following pairs of true functions f(x) and model classes h(x) determine: (i) if the model class is linear; (ii) if there is no under-fitting; and (iii) if there is no under-fitting, what is the true parameter?

(a) f(x) = 1 + 2x, and h(x) = w₀ + w₁x + w₂x²

(b) f(x) = 1 + x + 3x² + 4x³ , and h(x) = w₀ + w₁x + w₂x²