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الف) \((-\frac{6}{17}) + (-\frac{-8}{17}) = -\frac{6}{17} + \frac{8}{17} = \frac{2}{17}\)

ب) \((-\frac{12}{35}) - (+\frac{11}{42}) = -\frac{12}{35} - \frac{11}{42}\)
کوچک‌ترین مضرب مشترک مخرج‌ها ۲۱۰ است:
\[-\frac{12\times 6}{35\times 6} - \frac{11\times 5}{42\times 5} = -\frac{72}{210} - \frac{55}{210} = -\frac{127}{210}\]

پ) \((-\frac{2}{63}) - (-\frac{5}{72}) = -\frac{2}{63} + \frac{5}{72}\)
کوچک‌ترین مضرب مشترک ۵۰۴ است:
\[-\frac{2\times 8}{63\times 8} + \frac{5\times 7}{72\times 7} = -\frac{16}{504} + \frac{35}{504} = \frac{19}{504}\]

ت) \(-\frac{7}{12} + (-3) = -\frac{7}{12} - \frac{36}{12} = -\frac{43}{12}\)

ث) \((+\frac{2}{11}) \times (-\frac{6}{9}) = -\frac{2\times 6}{11\times 9} = -\frac{12}{99} = -\frac{4}{33}\)

ج) \((-\frac{1}{10}) \times (+\frac{8}{12}) = -\frac{1\times 8}{10\times 12} = -\frac{8}{120} = -\frac{1}{15}\)

چ) \(-8 \div (+5) = -\frac{8}{5} = -1\frac{3}{5}\)

ح) \((-12) \div (-28) = +\frac{12}{28} = \frac{3}{7}\)

خ) \((-\frac{7}{9}) \div (-\frac{28}{27}) = +\frac{7}{9} \times \frac{27}{28}\)
\[= \frac{7\times 27}{9\times 28} = \frac{7}{28}\times\frac{27}{9} = \frac{1}{4}\times 3 = \frac{3}{4}\]

د) \(-2/4 \div 1/2 = -\frac{1}{2} \div \frac{1}{2} = -\frac{1}{2} \times \frac{2}{1} = -1\)