Advertisements (Quảng cáo)
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. \(\left( {2x – 1} \right)\left( {3x + 2} \right)\left( {3 – x} \right)\)
a. \(\left( {{x^2} – 1} \right)\left( {{x^2} + 2x} \right)\) \( = {x^4} + 2{x^3} – {x^2} – 2x\)
Advertisements (Quảng cáo)
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. \(\left( {2x – 1} \right)\left( {3x + 2} \right)\left( {3 – x} \right)\) \( = \left( {6{x^2} + 4x – 3x – 2} \right)\left( {3 – x} \right)\)
\( = \left( {6{x^2} + x – 2} \right)\left( {3 – x} \right) = 18{x^2} – 6{x^3} + 3x – {x^2} – 6 + 2x = 17{x^2} – 6{x^3} + 5x – 6\)