a) (x + 2x + 1)(x + 1) = (3x + 1)(x + 1) = 3x$^{2}$ + 3x + x + 1 = 3x$^{2}$ + 4x + 1 ;
b) (x$^{3}$ - x$^{2}$ + 2x – 1)(5 – x) = -x$^{4}$ + x$^{3}$ - 2x$^{2}$ + x + 5x$^{3}$ - 5x$^{2}$ + 10x - 5 = -x$^{4}$ + 6x$^{3}$ - 7x$^{2}$ + 11x - 5.
$\Rightarrow$ (x – 5)(x$^{3}$ - x$^{2}$ + 2x – 1) = x$^{4}$ - 6x$^{3}$ + 7x$^{2}$ - 11x + 5.