Afla ca (9^1+9^2+9^3+....9^100)|10

Răspuns :

9^1+9^2+9^3+9^4+...+9^99+9^100 =
grupam termenii sumei cate doi
= (9^1+9^2)+(9^3+9^4)+...+(9^99+9^100)=

= 9^1×(1+9)+9^3×(1+9)+...+9^99×(1+9) =

= 10×(9^1+9^3+...+9^99) | 10