a)cho A = \(\frac{5}{4}\)+ \(\frac{5}{4^2}\)+ \(\frac{5}{4^3}\)+.......+ \(\frac{5}{4^{99}}\) .CHỨNG MINH RẰNG A < \(\frac{5}{3}\)
b)cho E = \(\frac{1}{3}\)+ \(\frac{2}{3^2}\)+ \(\frac{3}{3^3}\)+.......+ \(\frac{100}{3^{100}}\).CHỨNG MINH RẰNG E < \(\frac{3}{4}\)