Toán Lớp 8: a) ( 3$x^{2}$-6xy+9x) . 4/3xy =
b) 10$x^{3}$+2/5y- 1/3z – 1/2xy =
c) 5$x^{2}$ – 3x . ( x + 2 ) =
d) 3x . ( x – 5 ) – 5x . ( x + 7 ) =
e) 3$x^{2}$ . ( 2y – 1 ) – $x^{2}$ . ( 5y – 3 ) – 2x . ( x – 1 ) =
f) 3$x^{2}y$ . ( 2$x^{2}$ – 1 ) – 2$x^{2}$ . ( 2$x^{2}y$ – $y^{2}$ ) =
g) 4x . ( $x^{3}$ – 4$x^{2}$ ) + 2x . ( 2$x^{3}$ – $x^{2}$ + 7x ) =
h) 25x – 4 . ( 3x – 1 ) + 7x . ( 5 – 2$x^{2}$ ) =
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a)\left( {3{x^2} – 6xy + 9x} \right).\frac{4}{3}xy\\
= \left( {{x^2} – 2xy + 3x} \right).3.\frac{4}{3}xy\\
= \left( {{x^2} – 2xy + 3x} \right).4xy\\
= 4{x^3}y – 8{x^2}{y^2} + 12{x^2}y\\
b)10{x^3} + \frac{2}{5}y – \frac{1}{3}z – \frac{1}{2}xy\\
c)5{x^2} – 3x\left( {x + 2} \right)\\
= 5{x^2} – 3{x^2} – 6x\\
= 2{x^2} – 6x\\
d)3x\left( {x – 5} \right) – 5x\left( {x + 7} \right)\\
= 3{x^2} – 15x – 5{x^2} – 35x\\
= – 2{x^2} – 50x\\
e)3{x^2}\left( {2y – 1} \right) – {x^2}\left( {5y – 3} \right) – 2x\left( {x – 1} \right)\\
= 6{x^2}y – 3{x^2} – 5{x^2}y + 3{x^2} – 2{x^2} + 2x\\
= {x^2}y – 2{x^2} + 2x\\
f)3{x^2}y\left( {2{x^2} – 1} \right) – 2{x^2}\left( {2{x^2}y – {y^2}} \right)\\
= 6{x^4}y – 3{x^2}y – 4{x^4}y + 2{x^2}{y^2}\\
= 2{x^4}y + 2{x^2}{y^2} – 3{x^2}y\\
g)4x\left( {{x^3} – 4{x^2}} \right) + 2x\left( {2{x^3} – {x^2} + 7x} \right)\\
= 4{x^4} – 16{x^3} + 4{x^4} – 2{x^3} + 14{x^2}\\
= 8{x^4} – 18{x^3} + 14{x^2}\\
h)25x – 4\left( {3x – 1} \right) + 7x\left( {5 – 2{x^2}} \right)\\
= 25x – 12x + 4 + 35x – 14{x^3}\\
= – 14{x^3} + 48x + 4
\end{array}$