Question

Calculați suma:
2+4+6+...+98+100

Answer 1

Voi folosi formula lui Gauss :
1+2+....+n=(1+n)•n/2

2+4+........+98+100=(2+100)•50/2=102•50/2=102•25=2550
Deci suma este 2550

Answer 2

Dand factor comun avem:
2(1+2+3+...+50)

1+2+3+...+n=n(n+1)/2
1+2+3+...+50=50(50+1)/2=(50•51)/2=25•51=1275

2(1+2+3+...+50)=2•1275=2550