f=1+3²+3⁴+3⁶+....+3²⁰²²

\(E=\dfrac{5\times4^{15}\times9^9-4\times3^{20}\times8^9}{5\times2^{10}\times6^{19}-7\times2^{29}\times27^6}\)

\(C=\dfrac{5\times4^6\times9^4-3^9\times\left(-8\right)^4}{4\times2^{13}\times3^8+2\times8^4\times\left(-27\right)^3}\)

tìm các số tự nhiên a,b thỏa mãn điều kiện:\(\dfrac{11}{17}< \dfrac{a}{b}< \dfrac{23}{29}và8b-9b=31\)

\((\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{9}+\dfrac{1}{10})\times x=\dfrac{1}{9}+\dfrac{2}{8}+\dfrac{3}{7}+...+\dfrac{8}{2}+\dfrac{9}{1}\)

cho P =\(\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{9^2}cmr\dfrac{2}{5}< P< \dfrac{8}{9}\)