B- \[ \frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \frac{2}{7 \times 9} + \frac{2}{9 \times 11} + \frac{2}{11 \times 13} + \frac{2}{13 \times 15} + \frac{2}{1 \times 2} + \frac{2}{2 \times 3} + \frac{2}{3 \times 4} + \ldots + \frac{2}{8 \times 9} + \frac{2}{9 \times 10} \] c- \[ \frac{3}{1 \times 2} + \frac{3}{2 \times 3} + \frac{3}{3 \times 4} + \frac{3}{4 \times 5} + \ldots + \frac{3}{9 \times 10} + \frac{77}{2 \times 9} + \frac{77}{9 \times 16} + \frac{77}{16 \times 23} + \ldots + \frac{77}{93 \times 100} \] d- \[ \frac{4}{3 \times 6} + \frac{4}{6 \times 9} + \frac{4}{9 \times 12} + \frac{4}{12 \times 15} \]

----- Nội dung ảnh -----
b-
\[
\frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \frac{2}{7 \times 9} + \frac{2}{9 \times 11} + \frac{2}{11 \times 13} + \frac{2}{13 \times 15} + \frac{2}{1 \times 2} + \frac{2}{2 \times 3} + \frac{2}{3 \times 4} + \ldots + \frac{2}{8 \times 9} + \frac{2}{9 \times 10}
\]

c-
\[
\frac{3}{1 \times 2} + \frac{3}{2 \times 3} + \frac{3}{3 \times 4} + \frac{3}{4 \times 5} + \ldots + \frac{3}{9 \times 10} + \frac{77}{2 \times 9} + \frac{77}{9 \times 16} + \frac{77}{16 \times 23} + \ldots + \frac{77}{93 \times 100}
\]

d-
\[
\frac{4}{3 \times 6} + \frac{4}{6 \times 9} + \frac{4}{9 \times 12} + \frac{4}{12 \times 15}
\]