Question

din suma primelor 50 nr pare diferite de 0 scade suma primelor 50 nr impare

Answer 1

Suma lui gauss:

2+4+6+......+50=2×1+2×2+2×3+...........+2×25
=2×(1+2+3+.......+25)=2×(25×26:2)
=325×2=650 (suma nr pare)



1+3+5+..........+49=lasam 1 la final = (2×1+1)+(2×2+1)+........+(2×24+1)
=2×(24×25:2)+1×25= 600+25=625
=650-625=25.