Question

CUM SE REZOLVA 2+2^2+2^3+....+2^2005=?

Answer 1

adaug un doi in fata si scad un doi la sfarsit:
$2+2+ 2^{2} + 2^{3} +2^{4} +.....+2^{2005} -2=$
primii 2 termeni ii adun:
$2^{3} + 2^{3} +2^{4} +.....+2^{2005} -2=$
.................................
$2^{2005} +2^{2005} -2=2^{2006} -2$