Răspuns:
Explicație pas cu pas:
b) 1+2+3+.....+500 = (1+500)·500:2 = 501·250 = 125250
d) 1+2+3+.....+124 = (1+124)·124:2 = 125·62 = 7750
e) 2+4+6+....+600 = 2·(1+2+3+....+300) = 2·(1+300)·300:2 =
= 301·300 = 90300
f) 15+16+17+....+70 = (15+70)·(70-15+1):2 = 85·56:2 = 85·28 = 2380
g) 5+6+7+.....+81 = (5+81)·(81-5+1):2 = 86·77:2 = 43·77 = 3311
