Question

Fie progresia aritmetica in care a1=4,a5=22.Calculati a 10

Answer 1

a1 = 4
a5 = 22
_________
an = a1 + r • ( n-1 )
r- rația
a1 - primul termen
an - termen general
_________________
a5 = 4 + 4r
22 = 4 + 4r
-> 4r = 18 -> r =18/4 -> r = 9/2

-> a10 = 4 + 9 • 9/2
-> a10 = (8+81)/2
-> a10 = 89/2