Question

4+9+14+19+...+1004
Ma poate ajuta cineva

Answer 1

4+9+14+19+..............+1004
1004=4+(n-1)*5
1004=4+5n-5
5n=1004-4+5
5n=1005
n=1005/5
n=201
$S_{201}$=8+1000/2*201
$S_{201}$=1008/2*201
=504*201=101304

Answer 2

Este o progresie aritmetica de ratie 5
r=5
a1=4
an=a1+(n-1)r=1004
4+5n-5=1004
5n-1=1004
5n=1005
n=201

Sn=S201=(a1+a201)•201/2=1008•201/2=101304

a201=a1+200r=4+200•5=1004