A= 3x² y-11x²-5y.8xy-5+6

=(3-11-5.8-5+6).(x².x².x).(y.y.y)

=-47x⁵y³

a: \(=2x^2-x+5\)

b: \(=-\dfrac{3}{2}x^3+x^2-\dfrac{1}{2}x\)

c: \(=-x^3+\dfrac{3}{2}-2x\)

d: \(=-2x^2+4xy-6y^2\)

e: \(=\dfrac{3}{5}\left(x-y\right)^3-\dfrac{2}{5}\left(x-y\right)^2+\dfrac{3}{5}\)

cau a : (3x^2y-6xy+9x)(-4/3xy)

           =-4/3xy.3x^2y+4/3xy.6xy-4/3xy.9x

           =-4x+8-8y

cau b : (1/3x+2y)(1/9x^2-2/3xy+4y^2)

            =(1/3)^3-2/9x^2y+8y^3+4/3xy^2+2/9x^2y-4/3xy^2+8y^3

             =(1/3)^3 + (2y)^3x-2

cau c :  (x-2)(x^2-5x+1)+x(x^2+11)

            =x^3-5x^2+x-2x^2+10x-2+x^3+11x

            =2x^3-7x^2+22x-2

cau d := x^3 + 6xy^2 -27y^3

cau e := x^3 + 3x^2 -5x - 3x^2y - 9xy = 15y

cau f := x^2-2x+2x -4-2x-1

          = x(x-2)-5

cau e la + 15y ko phai =15y

a) Ta có: \(-2xy^2\cdot\left(x^3y-2x^2y^2+5xy^3\right)\)

\(=-2x^4y^3+4x^3y^4-10x^2y^5\)

b) Ta có: \(\left(-2x\right)\cdot\left(x^3-3x^2-x+1\right)\)

\(=-2x^4+6x^3+2x^2-2x\)

c) Ta có: \(3x^2\left(2x^3-x+5\right)\)

\(=6x^5-3x^3+15x^2\)

d) Ta có: \(\left(-10x^3+\frac{2}{5}y-\frac{1}{3}z\right)\cdot\left(-\frac{1}{2}xy\right)\)

\(=5x^4y-\frac{1}{5}xy^2+\frac{1}{6}xyz\)

e) Ta có: \(\left(3x^2y-6xy+9x\right)\cdot\left(-\frac{4}{3}xy\right)\)

\(=-4x^3y^2+8x^2y^2-12x^2y\)

f) Ta có: \(\left(4xy+3y-5x\right)\cdot x^2y\)

\(=4x^3y^2+3x^2y^2-5x^3y\)

A/\(\left(2x^3+y^2-7xy\right)4xy^2.\)

\(=8x^4y^2+4xy^4-28x^2y^3\)

B/\(\left(2x^3-x-1\right)\left(5x-2\right)\)

\(=10x^4-5x^2-5x-4x^3+2x+2\)

\(=10x^4-5x^3-3x-4x^3+2\)

C/\(\left(2x^2-3\right)\left(4x^4+6x^2+9\right)\)

\(=\left(2x^2-3\right)\left(2x+3\right)^2\)

D/\(\left(3x^2-2y\right)^3-\left(2x^2-y\right)^3\)

( Bài này áp dụng hằng đẳng thức là làm được ạ )

a: \(3x^2y\left(2x^2-xy+5y^2\right)=6x^4y-3x^3y^2+15x^2y^3\)

b: \(\left(x+2\right)\left(x^2+3x-4\right)\)

\(=x^3+3x^2-4x+2x^2+6x-8\)

\(=x^3+5x^2+2x-8\)

a: \(=49x^2-64-10\left(4x^2+12x+9\right)+5x\left(9x^2-12x+4\right)+4x\left(x^2-10x+25\right)\)

\(=49x^2-64-40x^2-120x-90+45x^3-60x^2+20x+4x^3-40x^2+100x\)

\(=49x^3-91x^2-154\)

b: \(=27x^3+189x^2+441x+343-125x^3+y^3+x^3+6x^2y+12xy^2+8y^3\)

\(=-97x^3+189x^2+441x+6x^2y+12xy^2+9y^3+343\)

P/s : Phá ngoặc ra là ok : 

a ) 

\(\left[4x-2\left(x-3\right)\right].\left(-3x\right)\)

\(=\left[4x-2x+6\right]\left(-3x\right)\)

\(=-12x^2+6x^2-18x\)

b ) 

\(3\left[x-3\left(4-2x\right)+8\right]\)

\(=3\left[x-12+6x+8\right]\)

\(=3\left[7x-4\right]\)

\(=21x-12\)

c ) 

\(5\left(3x^2-4y^3\right)+9\left(2x^2-y^3\right)\)

\(=15x^2-20y^3+18x^2-9y^3\)

\(=33x^2-29y^3\)

d ) 

\(3x^2\left(2y-1\right)-2x^2\left(5y-3\right)\)

\(=6x^2y-3x^2-10x^2y+6x^2\)

\(=-4x^2y+3x^2\)