14 Tính :a) (x+2)(x^2+2x-9) ; b) (x^2y-6)(x^2-5) ; c) (x+y)(xy-4+y)
d) (x^2y^2-x+3/4)(x-1/2) ; e) (2x^n+1-3y^n).2xy(x^n+1-2y^n).3xy
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@Nguyễn Huy Tú @DƯƠNG PHAN KHÁNH DƯƠNG@Nguyễn Thanh Hằng@Akai Haruma@Phùng Khánh Linh
\(14a.\left(x+2\right)\left(x^2+2x-9\right)=x^3+2x^2-9x+2x^2+4x-18=x^3+4x^2-5x-18\)
\(b.\left(x^2y-6\right)\left(x^2-5\right)=x^4y-5x^2y-6x^2+30\)
\(c.\left(x+y\right)\left(xy-4+y\right)=x^2y-4x+xy+xy^2-4y+y^2\)
\(d.\left(x^2y^2-x+\dfrac{3}{4}\right)\left(x-\dfrac{1}{2}\right)=x^3y^2-\dfrac{1}{2}x^2y^2-x^2+\dfrac{5}{4}x-\dfrac{3}{8}\)
\(e.\left(2x^n+1-3y^n\right)2xy\left(x^n+1-2y^n\right)3xy=6x^2y^2\left(2x^{2n}+2-4x^ny^n+x^n-2y^n-3x^ny^n-3y^n+6y^{2n}\right)\left(tự-nhân-nốt-nhé\right)\)
