Question

Am nevoie de ajutor, dau coroana​

Answer 1

1 + 2 + .. + 100 < n < 3 + 6 + .. + 180

100×101/2 < n < 3×(1 + 2 + .. + 60)

50×101 < n < 3×60×61/2

5050 < n < 5490

5490 - 5050 + 1 = 441 de numere verifica dubla inegalitate

Answer 2

Răspuns:

pentru paranteza folosim formula Gauss: 1+2+3...+n=n(n+1)/2

1 + 2 + .. + 100 < n < 3 + 6 + .. + 180

1 + 2 + .. + 100=100(100+1)/2=100·101:2=5050

3 + 6 + .. + 180=3·(1+2+3+...+60)=3·60·61:2=5490

5050 < n < 5490

5490-5050+1=441 de numere