1. 1+2+3+4+..........+100 =100×101/2 = 5050
daca, scrie 1+2+3+4+ .............=100 ⇒n(n+1)/2 =100 n(n+1) =200 n∉N (nu exista 2 numere consecutive al caror produs =200)
2. S2 =1+2+2²+2³+2^4+........2^7
2S2 =2+2²+2³+................+2^7+2^8
2S2 - S2 = S2 = 2^8 - 1 ⇒ S2 =(2^8 - 1) /2 = 1023/2
