Question

Fie a1=1, a4=7 termenii unei progresii aritmetitce. Calculati a2015 clasa 11

Answer 1

In general an=a1 + (n-1)r, deci 7=1 +(4-1)r, =>r=2.
Deci a2015=1 +(2015-1)2,=> a2015=4029

Answer 2

a1=1
a4=7
a4=a1+3r =>3r=a4-a1 --->3r=7-1=6 --->3r=6 |:3 =>r=2
a2015=a1+2014r =1+2014 *2--->a2015 =1+4028 =4029 --->a2015=4029