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Ta có : 5566 = [(11.5)6]11 = (116 . 56)11 = (115 . 11 . 56)11
6655 = [(11.6)5]11 = (115 . 65)11
Vì 11 . 56 > 65 nên 5566 > 6655
5566 > 6655
mk gthik chắc bn k hiểu nên tốt nhất mk k gthik
A = \(\dfrac{1}{3}\) + \(\dfrac{1}{6}\) + \(\dfrac{1}{10}\) + \(\dfrac{1}{15}\) + ..+ \(\dfrac{1}{55}\)+ \(\dfrac{1}{66}\)
A = 2 \(\times\) ( \(\dfrac{1}{6}\) + \(\dfrac{1}{12}\) + \(\dfrac{1}{20}\) + \(\dfrac{1}{30}\) +...+ \(\dfrac{1}{110}\) + \(\dfrac{1}{132}\))
A = 2 \(\times\) ( \(\dfrac{1}{2.3}\) + \(\dfrac{1}{3.4}\) + \(\dfrac{1}{4.5}\)+ \(\dfrac{1}{5.6}\) +...+ \(\dfrac{1}{10.11}\)+ \(\dfrac{1}{11.12}\))
A = 2 \(\times\) ( \(\dfrac{1}{2}\) - \(\dfrac{1}{3}\) + \(\dfrac{1}{3}\) - \(\dfrac{1}{4}\) + \(\dfrac{1}{4}\) - \(\dfrac{1}{5}\) + \(\dfrac{1}{5}\) - \(\dfrac{1}{6}\) +...+ \(\dfrac{1}{10}\) - \(\dfrac{1}{11}\)+ \(\dfrac{1}{11}\) - \(\dfrac{1}{12}\))
A = 2 \(\times\) ( \(\dfrac{1}{2}\) - \(\dfrac{1}{12}\))
A = 1 - \(\dfrac{1}{6}\) < 1
Vậy A = \(\dfrac{1}{3}\) + \(\dfrac{1}{6}\) + \(\dfrac{1}{10}\) + \(\dfrac{1}{15}\) + ...+ \(\dfrac{1}{55}\)+ \(\dfrac{1}{66}\) < 1
Ta có : 5566 = [(11.5)6]11 = (116 . 56)11 = (115 . 11 . 56)11
6655 = [(11.6)5]11 = (115 . 65)11
Vì 11 . 56 > 65 nên 5566 > 6655
\(55^{66}=\left(55^6\right)^{11}=\left[\left(11.5\right)^6\right]^{11}=\left(11^6.5^6\right)^{11}=\left(11^5.11.5^6\right)^{11}\)
\(66^{55}=\left(66^5\right)^{11}=\left[\left(11.6\right)^5\right]^{11}=\left(11^5.6^5\right)^{11}\)
Vì : \(11.5^6>6^5\)
Vậy : \(55^{66}>66^{55}\)