Question

Va rog!!!!!!!!!!!!!!!!!

Answer 1

Explicație pas cu pas:

S=1+3+3²+...+3⁸=>

3S=3+3²+3³+...+3⁸+3⁹=>

3S-S=3⁹-1=>2S=3⁹-1=>S=(3⁹-1)/2

2S<3⁹ => 2*(3⁹-1)/2<3⁹ => 3⁹-1<3⁹ (Adevarat)

Answer 2

Răspuns:

2(1+3+3^2+...+3^8)<3^9

S=1+3+3^2+...+3^8|*3

3S=3+3^2+3^3+...+3^9

________________________

3S-S= 3+3^2+3^3+...+3^9-1-3-3^2-...-3^8

2S= 3^9-1

S= (3^9-1)/2

2*(3^9-1)/2= 3^9-1<3^9