Least Squares: Finding a and b

The viewer can (1) say what the equation error ε is and why it's in the model, (2) compute ε(t) for given a, b and data, (3) write V(θ) and explain why squares, (4) derive the 2×2 normal equations by setting ∂V/∂a = ∂V/∂b = 0, (5) write the matrix form ε = y − Φθ and derive ΦᵀΦθ = Φᵀy, and say why y = Φθ cannot be solved directly.