Question

c=3+6+9+...+57
c=?
va rog

Answer 1

c = 3 + 6 + .. + 57

c = 3·(1 + 2 + .. + 19)

Aplicam formula lui Gauss

1 + 2 + .. + n = n·(n + 1) : 2 In cazul nostru n = 19

c = 3·(19·20 : 2)

c = 570