Câu trả lời:

Đây nha bạn:

$A=\genfrac{}{}{0ex}{}{2}{5.7}+\genfrac{}{}{0ex}{}{5}{7.12}+\genfrac{}{}{0ex}{}{7}{12.19}+\genfrac{}{}{0ex}{}{9}{19.28}+\genfrac{}{}{0ex}{}{11}{28.39}+\genfrac{}{}{0ex}{}{1}{39.40}$

$=\genfrac{}{}{0ex}{}{7-5}{5.7}+\genfrac{}{}{0ex}{}{12-7}{7.12}+\genfrac{}{}{0ex}{}{19-12}{12.19}+\genfrac{}{}{0ex}{}{28-19}{19.28}+\genfrac{}{}{0ex}{}{39-28}{28.39}+\genfrac{}{}{0ex}{}{40-39}{39.40}$

$=\genfrac{}{}{0ex}{}{1}{5}-\genfrac{}{}{0ex}{}{1}{7}+\genfrac{}{}{0ex}{}{1}{7}-\genfrac{}{}{0ex}{}{1}{12}+\genfrac{}{}{0ex}{}{1}{12}-\genfrac{}{}{0ex}{}{1}{19}+\genfrac{}{}{0ex}{}{1}{19}-\genfrac{}{}{0ex}{}{1}{28}+\genfrac{}{}{0ex}{}{1}{28}-\genfrac{}{}{0ex}{}{1}{39}+\genfrac{}{}{0ex}{}{1}{39}-\genfrac{}{}{0ex}{}{1}{40}$

=15−140=740=