Ma poate ajuta cineva la 1. Va rog

Răspuns:
1+3+5+...+99=(1+2+3+..+100)-(2+4+6+...+98+100)=100×101:2+2(1+2+3+..+49+50)=5050+2(50×51÷2)=5050+2×1275=5050+2550=7600