Consider the following model:E(Y|X) =β1X1+β2X2+β3X3AssumeX1+X2=X3. Show thatXTXfor this model is not invertible directly, that is, without using thefact that ifXis linearly dependent, thenXTXis linearly dependent.

Xtax=1. determine their canon- 1. write the following quadratic forms as v(x) ical forms, find the modal matrices (i.e. the matrices of unit eigenvectors) of the corresponding transformations and write down explicite expressions for canonical coordinates (y1, 2, y3) in terms of the original coordinates (x1, x2, x3). state what surfaces these quadratic forms correspond to: = > (a) -a x + 4x12 4x1x38x231; (b) 3-33 + 4xrj224x3122a3= 1; (c) 4a7 2x1 2x1x36x2a3 = 1. 2. solve the following systems of differential equations using the matrix exponential technique 3x 4 (a) x(0) = 5, y(0) = 1; 4x-3y 3.x y(0) = 9, y(0) = 3; -2x 6x2y