Ответ:

  1. Раскрываем скобки: \(3x\cdot4x^2-3x\cdot x=12x^3-3x^2\).
  2. \(-5a^2\cdot a^2+(-5a^2)\cdot(-6a)+(-5a^2)\cdot(-3)=-5a^4+30a^3+15a^2\).
  3. \(0.5b\cdot8b^2-0.5b\cdot10b+0.5b\cdot2=4b^3-5b^2+b\).
  4. \(x^3\cdot x^5-x^3\cdot x^2+x^3\cdot7x-x^3=x^8-x^5+7x^4-x^3\).
  5. \((-2c^2d^4)\cdot4c^2+(-2c^2d^4)\cdot(-c^3d)+(-2c^2d^4)\cdot5d^4=-8c^4d^4+2c^5d^5-10c^2d^8\).
  6. \((-4m^2n^8)\cdot5m^3n+(-4m^2n^8)\cdot(-8mn^2)+(-4m^2n^8)\cdot(-2n^6)=-20m^5n^9+32m^3n^{10}+8m^2n^{14}\).

Ответ: 1) \(12x^3-3x^2\); 2) \(-5a^4+30a^3+15a^2\); 3) \(4b^3-5b^2+b\); 4) \(x^8-x^5+7x^4-x^3\); 5) \(-8c^4d^4+2c^5d^5-10c^2d^8\); 6) \(-20m^5n^9+32m^3n^{10}+8m^2n^{14}\).