Question

Sa se calculeze suma primilor 5 termeni ai unei progresii aritmetrice stiind ca a1=1 si a2=3

Answer 1

yvyvugvug j fxr ywxyf jhhhhjjjj yfcyf

Answer 2

$r = a_{2} - a_{1} = 2$
$a_{5} = a_{1} + (5-1)r = 1 + 4*2 = 9$

$S_{5} = \frac{(a_{1} + a_{5})*5 }{2} = \frac{(1+9)*5 }{2} = \frac{10*5 }{2} = 25$

=> Suma primilor 5 termeni este 25.