Răspuns:
E(x) = (x+1)² - (x-1)²
E(x) = x²+2x+1 - ( x²-2x+1)
E(x) = 2x + 2x
E(x) = 4x
E(1) = 4
E(2) = 8
E(3) = 12
......
E(2009) = 8036
--------- +
4+8+12+.....+8036 = 4(1+2+......+2009)
= 4 * 2009 * 2010 / 2
= 2009 * 4020
