1)
a) - 9 + - 8 + .. 0 + 1 + .. + 6 = -9 + -8 + -7 = -24
b) -10 + -9 +.. + 0 + 1 + .. + 10 = 0
2)
S1= 1 - 2 + 3 - 4 + 5 - .... +99 - 100 = -1 -1 -1 .. -1 (de 50 ori )(am combinat tot 2 cate 2 1-2,3-4,5-6.. pana la 99-100) = -50
=> S1= -50.
S2 = -2-4-6 - 98 - 100 = -(2+4+6 + .. + 100) = - 2(1+2+..+50) = - 2 [ (50 x 51)/2 ] =
- (50 x 51) = - 2550
=> S2= -2550.