\(\begin{array}{l}a)\,\left( {2x - 1} \right)\left( {{x^2} + 5 - 4} \right) = \left( {2x - 1} \right)\left( {{x^2} + 1} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2{x^3} + 2x - {x^2} - 1\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,2{x^3} - {x^2} + 2x - 1\end{array}\)
\(\begin{array}{l}b)\, - \left( {5x - 4} \right)\left( {2x + 3} \right)\\ = \left( {4 - 5x} \right)\left( {2x + 3} \right)\\ = 8x + 12 - 10{x^2} - 15x\\ = - 10{x^2} - 7x + 12\end{array}\)
\(\begin{array}{l}c)\,7x\left( {x - 4} \right) - \left( {7x + 3} \right)\left( {2{x^2} - x + 4} \right)\\ = 7{x^2} - 28x - 14{x^3} + 7{x^2} - 28x - 6{x^2} + 3x - 12\\ = - 14{x^3} + 8{x^2} - 53x - 12\end{array}\)
