B1 : Tính giá trị biểu thức :
S = \(\frac{2}{1.3}\)- \(\frac{4}{3.5}\)+ \(\frac{6}{5.7}\)- \(\frac{8}{7.9}\)+ ... - \(\frac{96}{95.97}\)+ \(\frac{98}{97.99}\)
B2 : Chứng minh rằng A = \(\frac{1}{4}\)+ \(\frac{1}{16}\)+ \(\frac{1}{36}\)+ \(\frac{1}{64}\)+ \(\frac{1}{100}\)+ \(\frac{1}{144}\)+ \(\frac{1}{196}\)+ \(\frac{1}{256}\)+ \(\frac{1}{324}\)< \(\frac{1}{2}\)