Giải thích các bước giải:
$\eqalign{ & a)\,5x({x^2} - 2x + 3) \cr & = 5{x^3} - 10{x^2} + 15x \cr & b)\,({x^2} + 1)(5 - x) \cr & = {x^2}(5 - x) + 1(5 - x) \cr & = 5{x^2} - {x^3} + 5 - x \cr & = - {x^3} + 5{x^2} - x + 5 \cr & c)\,(x - 2)({x^2} + 3x - 4) \cr & = x({x^2} + 3x - 4) - 2({x^2} + 3x - 4) \cr & = {x^3} + 3{x^2} - 4x - (2{x^2} + 6x - 8) \cr & = {x^3} + 3{x^2} - 4x - 2{x^2} - 6x + 8 \cr & = {x^3} + {x^2} - 10x + 8 \cr & d)\,(x - 2)(x - {x^2} + 4) \cr & = x(x - {x^2} + 4) - 2(x - {x^2} + 4) \cr & = {x^2} - {x^3} + 4x - 2x + {x^3} - 8 \cr & = {x^2} + 2x - 8 \cr & e)\,({x^2} - 1)({x^2} + 2x) \cr & = {x^2}({x^2} + 2x) - ({x^2} + 2x) \cr & = {x^4} + 2{x^3} - {x^2} - 2x \cr & f)\,\left( {2x - 1} \right)\left( {3x + 2} \right)\left( {3 - x} \right) \cr & = \left( {2x - 1} \right)(9x + 6 - 3{x^2} - 2x) \cr & = \left( {2x - 1} \right)( - 3{x^2} + 7x + 6) \cr & = 2x( - 3{x^2} + 7x + 6) - ( - 3{x^2} + 7x + 6) \cr & = - 6{x^3} + 14{x^2} + 12x + 3{x^2} - 7x - 6 \cr & = - 6{x^3} + 17{x^2} + 5x - 6 \cr} $
