Question

Tính tổng: 

Answer 1

\(S=3+\frac{3}{2}+\frac{3}{2^2}+...+\frac{3}{2^9}\)

\(\Leftrightarrow2S=9+3+\frac{3}{2}+...+\frac{3}{2^8}\)

\(\Leftrightarrow2S-S=9-\frac{3}{2^9}\)

\(\Leftrightarrow S=9-\frac{3}{2^9}=\frac{4605}{512}\)

Vậy S = \(\frac{4605}{512}\)

Answer 2

S=3+3/2+3/2²+.....+3/2⁹

S=3.(1+1/2+1/2²+....+1/2⁹)

Đặt A=1+1/2+1/2²+......+1/2⁹)

Ta có:2A=2+1+1/2+....+1/2⁸

=>2A-A=(2+1+1/2+....+1/2⁸)-(1+1/2+1/2²+....+1/2⁹)

=>A=2-1/2⁹

Khi đó S=3.(2-1/2⁹)=6-3/2⁹=3069/512

Answer 3

cach giai luon nha

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