Ответ:

  1. \(12x^2-6x\).
  2. \(2x^2+4x\).
  3. \(2x^3-0.4x^2\).
  4. \(-2xy^3+x\).
  5. \(-0.5x^3+x^2-2x\).
  6. \(-90x^3-90x^2+0.9x\).
  7. \(3a^2c+3ac^2\).
  8. \(-a^4+a^2c^2\).
  9. \(-x^3y-2x^2y^2\).
  10. \(3a^2c^3+3a^2c^2-3ac^3\).
  11. \(-0.5x^3y^2-x^2y^3+0.5x^2y^2\).
  12. \(a^3c+2a^2c^2-ac^3\).
  13. \(-0.5x^3y^2-x^2y^3+0.5x^2y^2\).