Question

bn=3n+2
s40-?
помогите решить))

Answer 1

s40 = (bn•q-b1) : (q-1)

b1=3•1+2=5

b40 = 122

s40 = (122•40 - 5) : (40-1) = 4875 : 39 = 124

Answer 2

ой сории 125