Odpowiedź :
a1 = 2
r = 3
[tex]Sn = \frac{2a1 +( n-1) * r }{2} * n[/tex]
[tex]S10 = \frac{((2*2)+(10-1)*3)}{2} * 10= \frac{4 + 9*3}{2} * 10 = \frac{4+27}{2} * 10 = \frac{31}{2} * 10 = \frac{310}{2} = 155[/tex] SUMA
an = S10
an = a1 + (n − 1) ⋅ r
an = 2 + (n - 1) * 3
an = 2 + 3n - 3
an = 3n - 1
PODSTAWIAMY TERAZ DO WZORU
an = S10
3n - 1 = 155
3n = 155 + 1
3n = 156
n = 156 : 3
n = 52 <------------ Ten
spr. a52 = a1 + 51r = 2 + 51* 3= 2 + 153 = 155
Czy spisane są tu dobre odpowiedzi?