Question

XII.4.38. Se da sirul 1, 4, 7, 10, 13,..., 1 000,
Calculeaza al 100-lea termen al sirului. Câti termeni are sirul?

Answer 1

1,4,7,10,13,...,1000

Observam ca ratia=3 (merge din 3 in 3)

Sirul va avea (1000-1):3+1=999:3+1=334 termeni

Al 100-lea termen va fi egal cu: 1+3×99=298

Answer 2

Răspuns:

r=3

a100=a1+(n-1)r=1+99×3=1+297=298

1000=1+(n-1)3

999+3=3n

1002/3=334termeni