Question

Fie a1=1, a4=7 termenii unei progresii aritmetice. Calculati a2015.

Answer 1

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

Answer 2

a₁=1
a₄=7
a₂₀₁₅ -?
Folosim Formula Termenului General
an=a₁+(n-1)*r
Inlocuim
a₄=a₁+(4-1)*r
 7=1+(4-1)*r=>7=1+3*r=>3r=7-1=>3r=6=>r=2

Inlocuim in formula an=a₁+(n-1)*r
a ₂₀₁₅ =a₁+(2015-1)*r
          =1+(2014*2)=1+4028=4029