(4) (4 marks.) Let f(X1, X2, 23) = 3x] + 4x2 + 3x3 + 2x123. y1 (i) Find an orthogonal transformation 20 2 = P y2 that transforms y3 f(1, X2, 23) to the standard form in the new variables (i.e. the quadratic form containing only square terms in y1, y2, y3). (ii) Using the results in (i) show that the minimum value for f(1, X2, X3)/x x 2 1 with x = 20 2 * 0 is equal to 2. C 3