СРОЧНО ПОМОГИТЕ ДАЮ 30 БАЛЛОВ...

Решите задачу:

$\frac{7}{8}*\frac{8}{7}*\frac{9}{10}*\frac{10}{9}*\frac{11}{12}*\frac{12}{11}*\frac{13}{14}*\frac{14}{13}*\frac{15}{16}*\frac{16}{15}*\frac{17}{18}*\frac{18}{17}*\frac{19}{20}*\frac{20}{19}*\frac{21}{22}= \\\\ = \frac{7*8}{8*7}*\frac{9*10}{10*9}*\frac{11*12}{12*11}*\frac{13*14}{14*13}*\frac{15*16}{16*15}*\frac{17*18}{18*17}*\frac{19*20}{20*19}*\frac{21}{22} =\\\\ = 1*1*1*1*1*1*1*\frac{21}{22} = \\\\ = \frac{21}{22}$