Question

se considera sirul de numere naturale :3,7,11,15... aflati suma primelor 2015 numere

Answer 1

[tex]a1=3 a2=7 r=a2-a1=7-3=4[/tex]

$a2015=a1+2014r=3+2014*4=8059$

$S2015= \frac{3+8059}{2}*2015= \frac{8062}{2}*2015=4031*2015=8122465$