Question

calcule a soma dos 105 primeiros numeros pares nao negativos.

Answer 1

an = a1 + (n-1)*r
a105= 0+ (105-1)*2
a105= 104*2=208

0+2+4+6+8+10...+204+206+208=soma

Sn = (a1 + an)*n/2
S105= (0+208)*105/2
S105= 10920