Question

cate nr contine urmatorul sir 11,16,21,...2011?

Answer 1

(2016-11):5+1=2005:5+1=401+1=402

Answer 2

$r=5 \\ a_{1}=11 \\ a_{n} = 2011 \\ \\ a_{n} = a_{1} +r(n-1) \\ 2011 = 11+5(n-1) \\ 2011 = 11+5n-5 \\ 5n = 2011-11+5 \\ 5n = 2005 \\ n= \frac{2005}{5} \\ n=401$

=> sirul contine 401 termeni.