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# USAS - 12 #
\(=\frac{5}{3}.\frac{7}{5}.\frac{9}{7}......\frac{91}{89}\)
\(=\frac{91}{3}\)
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\(S=\left(1+\frac{2}{3}\right).\left(1+\frac{2}{5}\right)....\left(1+\frac{2}{89}\right)\)
\(\Rightarrow S=\frac{5}{3}.\frac{7}{5}....\frac{91}{89}\)
\(\Rightarrow S=\frac{5.7.9.....89.91}{3.5.7.....87.89}\)
\(\Rightarrow S=\frac{91}{3}\)
S=(1+\(\frac{2}{3}\))x(1+\(\frac{2}{5}\))x.....x(1+\(\frac{2}{89}\))
S=\(\frac{5}{3}\)x\(\frac{7}{5}\)x.....x\(\frac{91}{89}\)
KHỬ LIÊN TIẾP THÌ ĐƯỢC
S=\(\frac{91}{3}\)
\(S=\left(1+\frac{2}{3}\right)\cdot\left(1+\frac{2}{5}\right)\cdot\left(1+\frac{2}{7}\right)\cdot\cdot\cdot\left(1+\frac{2}{89}\right)\)
\(S=\frac{5}{3}\cdot\frac{7}{5}\cdot\frac{9}{7}\cdot\cdot\cdot\frac{91}{89}\)
\(S=\frac{5\cdot7\cdot9\cdot\cdot\cdot91}{3\cdot5\cdot7\cdot\cdot\cdot89}\)
\(S=\frac{5\cdot7\cdot9\cdot\cdot\cdot89\cdot91}{3\cdot5\cdot7\cdot\cdot\cdot89}\)
\(S=\frac{91}{3}\)