Nội dung bài giảng
Bài 76
a) \(\left( {2{x^2} - 3x} \right)\left( {5{x^2} - 2x + 1} \right)\)
b) \(\left( {x - 2y} \right)\left( {3xy + 5{y^2} + x} \right)\) .
Giải
a) \(\left( {2{x^2} - 3x} \right)\left( {5{x^2} - 2x + 1} \right)\)
= \(2{x^2}.5{x^2} - 2{x^2}.2x + 2{x^2}.1 - 3x.5{x^2} +(- 3x).(-2x) - 3x\)
= \(10{x^4} - 4{x^3} + 2{x^2} - 15{x^3} + 6{x^2} - 3x\)
= \(10{x^4} - 19{x^3} + 8{x^2} - 3x\)
b) \(\left( {x - 2y} \right)\left( {3xy + 5{y^2} + x} \right)\)
= \( x.3xy + x.5{y^2} + x.x - 2y.3xy - 2y.5{y^2} - 2y.x\) .
= \(3{x^2}y + 5x{y^2} + {x^2} - 6x{y^2} - 10{y^3} - 2xy\)
= \(3{x^2}y - x{y^2} - 2xy + {x^2} - 10{y^3}\)