Question

fie progresia aristmetica a1=5 si r=3 . Calculati a8 .

Answer 1

a2=a1+r, a3=a1+2r de aici, a8= a1+7r=5+3×7=5+21=26 . mai mult de explicat nu e.. e formula propriu-zisa

Answer 2

$a_1=5 \\ r=3 \\ a_8=? \\ a_8=a_{8-1}+r=a_7+r=a_1+7r=5+7 \cdot 3=5+21=26$