Làm tính nhân:
a. \(\left( {{x^2} - 1} \right)\left( {{x^2} + 2x} \right)\)
b. \(\left( {x + 3y} \right)\left( {{x^2} - 2xy + y} \right)\)
c. \(\left( {2x - 1} \right)\left( {3x + 2} \right)\left( {3 - x} \right)\)
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a. \(\left( {{x^2} - 1} \right)\left( {{x^2} + 2x} \right)\) \( = {x^4} + 2{x^3} - {x^2} - 2x\)
b. \(\left( {x + 3y} \right)\left( {{x^2} - 2xy + y} \right)\) \( = {x^3} - 2{x^2}y + xy + 3{x^2}y - 6x{y^2} + 3{y^2}\)
\( = {x^3} + {x^2}y + xy - 6x{y^2} + 3{y^2}\)
c. \(\left( {2x - 1} \right)\left( {3x + 2} \right)\left( {3 - x} \right)\) \( = \left( {6{x^2} + 4x - 3x - 2} \right)\left( {3 - x} \right)\)
\( = \left( {6{x^2} + x - 2} \right)\left( {3 - x} \right) = 18{x^2} - 6{x^3} + 3x - {x^2} - 6 + 2x = 17{x^2} - 6{x^3} + 5x - 6\)