Toán Lớp 8: thực hiện phép tính
a, 5x^2(3x^2-4xy+2y^2)
b, (6x^2y^3-9x^3y^2+15x^2y^2);3x^2y
c, 5x+10/4x-8 .4-2x/x+2
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Toán Lớp 8: thực hiện phép tính
a, 5x^2(3x^2-4xy+2y^2)
b, (6x^2y^3-9x^3y^2+15x^2y^2);3x^2y
c, 5x+10/4x-8 .4-2x/x+2
Comments ( 1 )
a)\\
5{x^2}(3{x^2} – 4xy + 2{y^2})\\
= \left( {5{x^2}.3{x^2}} \right) – \left( {5{x^2}.4xy} \right) + \left( {5{x^2}.2{y^2}} \right)\\
= 15{x^4} – 20{x^3}y + 10{x^2}{y^2}\\
b)(6{x^2}{y^3} – 9{x^3}{y^2} + 15{x^2}{y^2}):3{x^2}y\\
= \left( {6{x^2}{y^3}:3{x^2}y} \right) – \left( {9{x^3}{y^2}:3{x^2}y} \right) + \left( {15{x^2}{y^2}:3{x^2}y} \right)\\
= 2{y^2} – 3xy + 5y\\
c)\dfrac{{5x + 10}}{{4x – 8}}.\dfrac{{4 – 2x}}{{x + 2}}\\
= \dfrac{{5\left( {x + 2} \right)}}{{4\left( {x – 2} \right)}}.\dfrac{{2\left( {2 – x} \right)}}{{x + 2}}\\
= \dfrac{{10\left( {x + 2} \right)\left( {x – 2} \right)}}{{4\left( {x – 2} \right)\left( {x + 2} \right)}}\\
= \dfrac{{10}}{4}\\
= \dfrac{5}{2}
\end{array}\]