Thực hiện phép tính:
a) \((9{x^4} - 12{x^3} + 6{x^2}):3{x^2}\) ;
b) \((24{x^5} + 12{x^4} - 7{x^3}):6{x^3}\) ;
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c) \((15{x^3}{y^3} + 12{x^2}{y^4} - 9{x^2}{y^2}):3{x^2}{y^2}\).
\(\eqalign{ & a)\,\,\left( {9{x^4} - 12{x^3} + 6{x^2}} \right):\left( {3{x^2}} \right) = {{9{x^4}} \over {3{x^2}}} - {{12{x^3}} \over {3{x^2}}} + {{6{x^2}} \over {3{x^2}}} = 3{x^2} - 4x + 2 \cr & b)\,\,\left( {24{x^5} + 12{x^4} - 7{x^3}} \right):\left( {6{x^3}} \right) = {{24{x^5}} \over {6{x^3}}} + {{12{x^4}} \over {6{x^3}}} - {{7{x^3}} \over {6{x^3}}} = 4{x^2} + 2x - {7 \over 6} \cr & c)\,\,\left( {15{x^3}{y^3} + 12{x^2}{y^4} - 9{x^2}{y^2}} \right):\left( {3{x^2}{y^2}} \right) = {{15{x^3}{y^3}} \over {3{x^2}{y^2}}} + {{12{x^2}{y^4}} \over {3{x^2}{y^2}}} - {{9{x^2}{y^2}} \over {3{x^2}{y^2}}} = 5xy + 4{y^2} - 3 \cr} \)