A=1/3+1/9+1/27+1/81+......+1/95049

Ax3=3x(1/3+1/9+1/27+1/81+.........+1/95049)

Ax3=1+1/3+1/9+1/27+1/81+..........+1/19683

Ax3-A=1+1/3+1/9+1/27+1/81+............+1/19683

- (1+1/3+1/9+1/27+1/81+........+1/59049)

=1-1/59049

2xA=59048/59049

A=59048/59049:2

A=29524/59049

giúp với help me

ta có :

= ( 1 + 59049 ) + ( 3 + 2187 ) + ( 9 + 6561 ) + ( 27 + 243 ) + ( 81 + 729 )

= 59050 + 2190 + 6570 + 270 + 810

= 59050 + ( 2190 + 810 ) + 6570 + 270

= 59050 + 3000 + 6570 + 270

= 59050 + ( 3000 + 6570 ) + 270

= 59050 + 9570 + 270

= 68620 + 270

= 68890

68890

 Đặt   \(A=\frac{1}{3}+\frac{1}{9}+.......+\frac{1}{59049}\)

  \(3A=3.\left(\frac{1}{3}+\frac{1}{9}+......+\frac{1}{59049}\right)\)

\(3A=1+\frac{1}{3}+........+\frac{1}{19683}\)

\(3A-A=\left(1+\frac{1}{3}+......+\frac{1}{19683}\right)-\left(\frac{1}{3}+\frac{1}{9}+........+\frac{1}{59049}\right)\)

\(2A=1-\frac{1}{59049}\)

\(2A=\frac{59048}{59049}\)

\(A=\frac{59048}{59049}:2\)

\(A=\frac{59048}{118098}\)

tuyên truyền ae chửi báo cáo sai phạm con girl yêu

đừng để nó thôi miên

rất cảm ơn ! gà con ; 1234 ; ...

họ là người tốt đừng để thôi miên 

Bài 1:

Bài 1: 1/3+1/9+1/27+1/81+1/243+1/729

Đặt:
A = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729
Nhân A với 3 ta có:
\(Ax3=3+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)
\(\Rightarrow Ax3-S=3-\frac{1}{243}\)
\(\Rightarrow2A=\frac{2186}{729}\)
\(\Rightarrow A=\frac{2186}{729}:2\)
\(\Rightarrow A=\frac{1093}{729}\)

a: Đặt \(A=\frac15+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+\cdots+\frac{1}{1280}\)

=>\(2\times A=\frac25+\frac15+\frac{1}{10}+\frac{1}{20}+\cdots+\frac{1}{640}\)

=>\(2\times A-A=\frac25+\frac15+\frac{1}{10}+\frac{1}{20}+\cdots+\frac{1}{640}-\frac15-\frac{1}{10}-\frac{1}{20}-\cdots-\frac{1}{1280}\)

=>\(A=\frac25-\frac{1}{1280}=\frac{511}{1280}\)

b: Đặt \(B=\frac13+\frac19+\frac{1}{27}+\cdots+\frac{1}{59049}\)

=>\(3\times B=1+\frac13+\frac19+\frac{1}{27}+\cdots+\frac{1}{19683}\)

=>\(3\times B-B=1+\frac13+\frac19+\frac{1}{27}+\cdots+\frac{1}{19683}-\frac13-\frac19-\frac{1}{27}-\cdots-\frac{1}{59049}\)

=>2xB=\(1-\frac{1}{59049}=\frac{59048}{59049}\)

=>\(B=\frac{29524}{59409}\)

c: \(\frac12\times3+\frac13\times4+\frac14\times5+\frac15\times6\)

\(=\frac32+\frac43+\frac54+\frac65\)

\(=\frac{90}{60}+\frac{80}{60}+\frac{75}{60}+\frac{72}{60}=\frac{317}{60}\)