Question

cum se calculează exercițiu 5+10+15+...+100

Answer 1

5 + 10 + 15 + 20 + ......... + 100 = 1 050

→ progresie aritmetica de ratie = 5 ( 10 -5; 15 - 10 ....)

( 100 - 5 ) : 5 + 1 = 95 : 5 + 1 = 19 + 1 = 20 termeni are suma

→ aplic formula sumei lui Gauss:

= 20 × ( 5 + 100 ) / 2 =

= 10 × 105 =

= 1 050 → suma

Answer 2

S=5+10+15+...+100
S=5(1+2+3+...+20)
n×(n+1):2
S=5×20×(20+1):2
S=5×20×21:2
S=100×21:2
S=2100:2
S=1050