Question

1+3+3^2+3^3+...+3^10=x ,найти 3^4+3^5+...+3^15

Answer 1

$3^0 + 3^1 + 3^2 + \ldots + 3^{10} = x\\3^4 + 3^5 + \ldots + 3^{15} = 3^4(3^0 + 3^1 + \ldots + 3^{10}) + 3^{15} = \boxed{3^4x + 3^{15}}$