Ответ:

  1. Знаменатели равны, складываем числители: \(\frac{1}{7}+\frac{3}{7}=\frac{4}{7}\).
  2. \(\frac{11}{15}-\frac{7}{15}=\frac{4}{15}\).
  3. \(\frac{3}{7}+\frac{a}{7}=\frac{3+a}{7}\).
  4. \(\frac{2}{9}+\frac{x}{9}=\frac{2+x}{9}\).
  5. \(\frac{1}{10}+\frac{2x}{10}=\frac{1+2x}{10}\).
  6. \(\frac{x}{5}-\frac{2}{5}=\frac{x-2}{5}\).
  7. \(\frac{a}{3}+\frac{b}{3}=\frac{a+b}{3}\).
  8. \(\frac{2a}{11}-\frac{b}{11}=\frac{2a-b}{11}\).
  9. \(\frac{y^2}{8}-\frac{1}{8}=\frac{y^2-1}{8}\).
  10. \(\frac{6}{x}+\frac{2}{x}=\frac{8}{x}\).
  11. \(\frac{3a}{x}-\frac{4}{x}=\frac{3a-4}{x}\).
  12. \(\frac{2x^2}{y^3}+\frac{x}{y^3}=\frac{2x^2+x}{y^3}\).
  13. \(\frac{5b}{a^2}-\frac{3b}{a^2}=\frac{2b}{a^2}\).
  14. \(\frac{x}{2y}-\frac{a}{2y}=\frac{x-a}{2y}\).
  15. \(-\frac{2a}{b^2}+\frac{a}{b^2}=-\frac{a}{b^2}\).