Question

Determinati ultima cifră a Nr n unde n=1+1+2+2^2+2^3+2^4......+2^2018

Answer 1

n=1 +(1+2+2^2+2^3+2^4......+2^2018)

n=1 +2^2019  -1

n=2^2019

2019=4•504+3

u(n)=u(2^2019)=u[2^(4•504 +3)]=u(2^3)=8

Am utilizat formula:

1+a+a²+a³+…..+aⁿ=[a^(n+1)-1]/(a-1)