\(A=1+3^2+3^4+...+3^{2006}\)
\(3^2.A=3^2+3^4+3^6+...+3^{2008}\)
\(3^2.A-A=\left(3^2+3^4+3^6+...+3^{2008}\right)-\left(1+3^2+3^4+...+3^{2006}\right)\)
\(9.A-A=3^{2008}-1\)
\(8.A=3^{2008}-1\)
\(A=\frac{3^{2008}-1}{8}\)
Ủng hộ mk nha ^_-
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Ta có A = 1 + 32 + 34 + ...... + 32006
=> 32A = 32 + 34 + ...... + 32008
=> 9A = 32 + 34 + ...... + 32008
=> 9A - A = (32 + 34 + ...... + 32008) - (1 + 32 + 34 + ...... + 32006)
=> 8A = 32008 - 1
=> A = \(\frac{3^{2008}-1}{8}\)
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