51. \(-2\frac{1}{2} - 1\frac{2}{3}\)

Решение:

\(-2\frac{1}{2} - 1\frac{2}{3} = -\frac{5}{2} - \frac{5}{3} = -\frac{5 \times 3}{2 \times 3} - \frac{5 \times 2}{3 \times 2} = -\frac{15}{6} - \frac{10}{6} = -\frac{25}{6}\)

Ответ: -\(\frac{25}{6}\)