Đề bài
Làm tính nhân:
a) \(3x(5{x^2} - 3x + 2)\) ;
b) \({3 \over 5}{x^2}y(2{x^3}y + 5xy - 10{y^2})\) ;
c) \((4x + 3)({x^2} + 7x - 2)\) ;
d) \((x - 3y)(2xy - 5{y^2} + 4x)\).
Lời giải chi tiết
\(\eqalign{ & a)\,\,3x\left( {5{x^2} - 3x + 2} \right) \cr & \,\,\,\,\, = 3x.5{x^2} + 3x\left( { - 3x} \right) + 3x.2 \cr & \,\,\,\,\, = 15{x^3} - 9{x^2} + 6x \cr & b)\,\,{3 \over 5}{x^2}y\left( {2{x^3}y + 5xy - 10{y^2}} \right) \cr & \,\,\,\,\, = {3 \over 5}{x^2}y.2{x^3}y + {2 \over 3}{x^2}y.5xy + {3 \over 5}{x^2}y\left( { - 10{y^2}} \right) \cr & \,\,\,\,\, = {6 \over 5}{x^5}{y^2} + 3{x^3}{y^2} - 6{x^2}{y^3} \cr & c)\,\,\,\left( {4x + 3} \right)\left( {{x^2} + 7x - 2} \right) \cr & \,\,\,\,\, = 4{x^3} + 28{x^2} - 8x + 3{x^2} + 21x - 6 \cr & \,\,\,\,\, = 4{x^3} + 31{x^2} + 13x - 6 \cr & d)\,\,\left( {x - 3y} \right)\left( {2xy - 5{y^2} + 4x} \right) \cr & \,\,\,\,\, = 2{x^2}y - 5x{y^2} + 4{x^2} - 6x{y^2} + 15{y^3} - 12xy \cr & \,\,\,\,\, = 2{x^2}y - 11x{y^2} + 4{x^2} + 15{y^3} - 12xy \cr} \)
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