1. Express each of the following in summation notation (i.e. they should look like the questions in question (2) below). (1 mark each) (a) Xi + X2 + X3+ X4 (b) xy + X2y2 + X3y3 + X4y4 (c) " + (d) (X1-y1)+ (X2-y2) + (x3-y3) 2. Expand each of the following sums (i.e. when you "expand" them they should look like what you see in question (1), above, except that you should get an actual number for question (a) below. (1 mark each) 2. (a) (x +2x+ 2) x=0 (b) Ef(x, y) (C) x+ 2) y=1 X=2