Suppose we fit the model y x1beta1 epsilon when the true

Question

Questions on multiple linear regression models:

Suppose we fit the model y = X₁β₁+ ε when the true model is actually given by y = X₁β₂ + X₂β₂ + ε. For both models, assume E(ε) = 0 and Var(ε) = σ²I. where I is the identity matrix.

Find the expected value and variance of the ordinary least-squares estimate.

(Note here X,I are matrices, and y,β,ε are vectors since those are multiple linear models).