Đáp án:
\(\begin{array}{l}
B2:\\
a)2x{\left( {x - 5} \right)^2}\\
c)\left( {3x - 1 - 2y} \right)\left( {3x - 1 + 2y} \right)\\
b)\left( {3a - 2} \right)\left( {2a + 1} \right)\\
d)\left( {5x - 2y} \right).5x
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
B2:\\
a)2{x^3} - 20{x^2} + 50x\\
= x\left( {2{x^2} - 20x + 50} \right)\\
= 2x\left( {{x^2} - 5x - 5x + 25} \right)\\
= 2x\left( {x\left( {x - 5} \right) - 5\left( {x - 5} \right)} \right)\\
= 2x{\left( {x - 5} \right)^2}\\
c)9{x^2} - 6x + 1 - 4{y^2}\\
= {\left( {3x - 1} \right)^2} - 4{y^2}\\
= \left( {3x - 1 - 2y} \right)\left( {3x - 1 + 2y} \right)\\
b)9{a^2} - 4 - \left( {3a - 2} \right)\left( {a + 1} \right)\\
= \left( {3a - 2} \right)\left( {3a + 2} \right) - \left( {3a - 2} \right)\left( {a + 1} \right)\\
= \left( {3a - 2} \right)\left( {3a + 2 - a - 1} \right)\\
= \left( {3a - 2} \right)\left( {2a + 1} \right)\\
d){\left( {3x - y} \right)^2} - {\left( {2x + y} \right)^2}\\
= \left( {3x - y - 2x - y} \right)\left( {3x - y + 2x + y} \right)\\
= \left( {5x - 2y} \right).5x
\end{array}\)
