Đáp án:
5) 7
Giải thích các bước giải:
\(\begin{array}{l}
1)\left( {5{x^3} - {x^2} + 2x - 3} \right)\left( {4{x^2} - x + 2} \right)\\
= 20{x^5} - 5{x^4} + 10{x^3} - 4{x^4} + {x^3} - 2{x^2} + 8{x^3} - 2{x^2} + 4x - 12{x^2} + 3x - 6\\
= 20{x^5} - 9{x^4} + 19{x^3} - 16{x^2} + 7x - 6\\
2)\left( {x - 3} \right)\left( {x + 7} \right) - \left( {2x - 5} \right)\left( {x - 1} \right)\\
= {x^2} + 4x - 21 - 2{x^2} + 7x - 5\\
= - {x^2} + 11x - 26\\
3)\left( {3x + 5} \right)\left( {2x - 2} \right) + \left( {4x - 1} \right)\left( {3x + 2} \right)\\
= 6{x^2} + 4x - 10 + 12{x^2} + 5x - 2\\
= 18{x^2} + 9x - 12\\
4)\left( {3x - 1} \right)\left( {2x + 7} \right) - \left( {x + 1} \right)\left( {6x - 5} \right) - 2\left( {18x - 12} \right)\\
= 6{x^2} + 19x - 7 - 6{x^2} - x + 5 - 36x + 24\\
= - 18x + 22\\
5)\left( {{x^2} - 7} \right)\left( {x + 2} \right) - \left( {2x - 1} \right)\left( {x - 14} \right) - x\left( {{x^2} + 22} \right) + 35\\
= {x^3} + 2{x^2} - 7x - 14 - 2{x^2} + 29x - 14 - {x^3} - 22x + 35\\
= 7
\end{array}\)
