Nhân với S với 32 ta dc
9S = 3 ^ 2 + 3 ^ 4 + ... + 3 ^ 2002 + 3 ^ 2004
=> 9S - S = ( 3 ^ 2 + 3 ^ 4 + ... + 3 ^ 2004 ) - ( 3 ^ 0 + 3 ^ 4 + ... + 3 ^ 2002 )
=> 8S = 32004 - 1 : 8
=> S = 32004- 1 : 8
\(S=1+3^2+3^3+...+3^{2002}\)
\(3S=3+3^2+3^3+3^4+...+3^{2002}+3^{2003}\)
\(3S-S=\left(3+3^2+3^3+3^4+....+3^{2002}+3^{2003}\right)-\left(1+3^2+3^3+...+3^{2002}\right)\)
\(3S-S=3+3^2+3^3+3^4+....+3^{2002}+3^{2003}-1-3^2-3^3-...-3^{2002}\)
\(2S=3^{2003}-1\)
\(S=\frac{3^{2003}-1}{2}\)
S=1+32+34+36+...+32002-
32.S=32+34+36+38+...+32004
32.S-S= 8S=32004-1
Vậy S=\(\frac{3^{2004}-1}{8}\)
Ta có :
\(3^2S=3^2+3^4+3^6+....+3^{2004}\)
\(8S=3^{2004}-1\)
\(=>S=\frac{3^{2004}-1}{8}\)
Ủng hộ nha
Thank you very much
9S = \(9.\left(3^0+3^2+...+3^{2002}\right)\)
=> 9S = \(3^2+3^4+...+3^{2002}+3^{2004}\)
=> 9S - S = 8S = \(\left(3^2+3^4+..+3^{2004}\right)-\left(3^0+3^2+...+3^{2002}\right)\)
=> 8S = \(3^{2004}-1\)
=> S = \(\left(3^{2004}-1\right):8\)