Determine whether the following models are linear in the parameters, or the variables, or both. Which of these models are linear regression models?
(a) yi = a + b/xi + ui
(b) yi = a + b*log (xi) + ui
(c) log (yi) = a +b*xi + ui
(d) log (yi) = a + b*log (xi) + ui
(e) log (yi) = a - b/xi+ ui
(ui is the residual, which is the unsystematic part of yi and a + b*xi is the systematic part of yi