1 1x2 2 2x4 3 4x7

Lời giải:

 \(A = \frac{1}{{1 \times 2}} + \frac{2}{{2 \times 4}} + \frac{3}{{4 \times 7}} + \frac{4}{{7 \times 11}} + \frac{5}{{11 \times 16}} + \frac{6}{{16 \times 22}} + \frac{7}{{22 \times 29}}\)

\( = 1 - \frac{1}{2} + \frac{1}{2} - \frac{1}{4} + \frac{1}{4} - \frac{1}{7} + \frac{1}{7} - \frac{1}{{11}} + \frac{1}{{11}} - \frac{1}{{16}} + \frac{1}{{16}} - \frac{1}{{22}} + \frac{1}{{22}} - \frac{1}{{29}}\)

\( = 1 - \frac{1}{{29}} = \frac{{28}}{{29}}\)