Ответ:

  1. \(\frac{3x+3}{x+1}=\frac{3(x+1)}{x+1}=3\), \(x\ne-1\).
  2. \(\frac{2x-8}{x-4}=\frac{2(x-4)}{x-4}=2\), \(x\ne4\).
  3. \(\frac{x+7}{49-x^2}=\frac{x+7}{(7-x)(7+x)}=\frac{1}{7-x}\), \(x\ne\pm7\).
  4. \(\frac{-5-x}{(x+5)(x-5)}=\frac{-(x+5)}{(x+5)(x-5)}=-\frac{1}{x-5}\), \(x\ne\pm5\).
  5. \(\frac{y-3}{(y-3)(y+3)}=\frac{1}{y+3}\), \(y\ne\pm3\).
  6. \(\frac{y^2-6y+9}{y-3}=\frac{(y-3)^2}{y-3}=y-3\), \(y\ne3\).
  7. \(\frac{2+y}{y^2-4}=\frac{y+2}{(y-2)(y+2)}=\frac{1}{y-2}\), \(y\ne\pm2\).
  8. \(\frac{3-y}{y^2-9}=\frac{-(y-3)}{(y-3)(y+3)}=-\frac{1}{y+3}\), \(y\ne\pm3\).
  9. \(\frac{2-x+x+y}{4-y^2}=\frac{y+2}{(2-y)(2+y)}=\frac{1}{2-y}\), \(y\ne\pm2\).
  10. \(\frac{y^2+36-12y}{(6-y)^2}=\frac{(y-6)^2}{(6-y)^2}=1\), \(y\ne6\).

Ответ: 1) 3; 2) 2; 3) \(\frac{1}{7-x}\); 4) \(-\frac{1}{x-5}\); 5) \(\frac{1}{y+3}\); 6) \(y-3\); 7) \(\frac{1}{y-2}\); 8) \(-\frac{1}{y+3}\); 9) \(\frac{1}{2-y}\); 10) 1.