Consider the following nonstochastic models (i.e., models without the stochastic error term). Are they linear regression models? If not, is it possible, by suitable algebraic manipulations, to convert them into linear models?

a. Y_i = 1 / β₁ + β₂X_i

b. Y_i = X_i / β₁ + β₂X_i

c. Y_i = 1 / {1 + exp (-β₁ – β₂X_i)}