D  nhá!!

(-3*x-1)*y+3*x^2+x

D.(x - y)(3x + 1)

A = (3x - x + 1) - (2x - y + 5)

= 3x - x + 1 - 2x + y - 5

= y - 4

chấm đúng cho mình nhé😀😉😙

\(\left(x+2y\right)^2-\left(x-2y\right)^2\\ =\left[\left(x+2y\right)-\left(x-2y\right)\right]\left[\left(x+2y\right)+\left(x-2y\right)\right]\\ =\left(x+2y-x+2y\right)\left(x+2y+x-2y\right)\\ =4y.\left(2x\right)\\ =8xy\)

\(\left(3x+y\right)^2+\left(x-y\right)^2\\ =\left[\left(3x\right)^2+2.3x.y+y^2\right]+\left(x^2-2xy+y^2\right)\\ =6x^2+6xy+y^2+x^2-2xy-y^2\\ =7x^2+4xy\)

\(-\left(x+5\right)^2-\left(x-3\right)^2\\ =-\left(x^2+10x+25\right)-\left(x^2-6x+9\right)\\ =-x^2-10x-25-x^2+6x-9\\ =-2x^2-4x-34\)

\(\left(3x-2\right)^2-\left(3x-1\right)^2\\ =\left[\left(3x-2\right)-\left(3x-1\right)\right]\left[\left(3x-2\right)+\left(3x-1\right)\right]\\ =\left(3x-2-3x+1\right)\left(3x-2+3x-1\right)\\ =-1.\left(6x-3\right)\\ =-6x+3\)

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

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

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

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

\(=y^2\)

a) 3.(x+y).(x-y)+(x+y)^2+(x-y)^2

=3.(x²-y²)+(x²+2xy+y²)+(x²-2xy+y²)

=3x²-3y²+x²+2xy+y²+x²-2xy+y²

=5x²-y²
b) (2x+y)^2 - (y+3x)^2

=[(2x+y)+(y+3x)][(2x+y)-(y+3x)]

=(2x+y+y+3x)(2x+y-y-3x)

=(5x+2y)(-x)

=-5x²-2xy

Lời giải:
a. $(x+y)-(x-y)=x+y-x+y=(x-x)+y+y=0+2y=2y$

b. $3x(5x^2-2x-1)-15x^3=15x^3-6x^2-3x-15x^3=-6x^2-3x$
c. $(5x-2y)(x^2-xy+1)+7x^2y=5x^3-5x^2y+5x-2x^2y+2xy^2-2y+7x^2y$

$=5x^3+(-5x^3y-2x^2y+7x^2y)+5x+2xy^2-2y$

$=5x^3+5x+2xy^2-2y$

\(A=\left(2x+y\right)^2+\left(2x-y\right)^2+\left(4x^2-y^2\right)+3y\\ =\left(4x^2+4xy+y^2\right)+\left(4x^2-4xy+y^2\right)+\left(4x^2-y^2\right)+3y\\ =4x^2+4x^2+4x^2+4xy-4xy+y^2+y^2-y^2+3y=12x^2+3y-y^2\\ B=\left(x-2\right)\left(x+2\right)-\left(x+2\right)^2\\ =\left(x+2\right)\left(x-2-x-2\right)=-4\left(x+2\right)=-4x-8\\ C=\left(3x-4y\right)^2+\left(3x-4y\right)^2\\ =\left(9x^2-24xy+16y^2\right)+\left(9x^2-24xy+16y^2\right)\\ =18x^2-48xy+32y^2\)

A = x-y/x.(x+y) - 3x+y/x.(x-y) . (y-x)/x+y

   = x-y/x.(x+y) + 3x+y/x.(x+y)

   = x-y+3x+y/x.(x+y)

   = 4x/x.(x+y)

    = 4/x+y

Tk mk nha

\(A=\frac{x-y}{xy+y^2}-\frac{3x+y}{x^2-xy}.\frac{y-x}{x+y}\)

    \(=\frac{x-y}{y\left(x+y\right)}-\frac{3x+y}{x\left(x-y\right)}.\frac{-\left(x-y\right)}{x+y}\)

     \(=\frac{x-y}{y\left(x+y\right)}-\frac{-\left(3x+y\right).\left(x-y\right)}{x\left(x-y\right).\left(x-y\right)}\)

      \(=\frac{x-y}{y\left(x+y\right)}-\frac{-\left(3x+y\right)}{x\left(x-y\right)}\)

       \(=\frac{x\left(x-y\right)^2}{xy\left(x+y\right)\left(x-y\right)}+\frac{y\left(3x+y\right)\left(x+y\right)}{xy\left(x+y\right)\left(x-y\right)}\)

\(=\frac{x\left(x^2-2xy+y^2\right)+y\left(3x^2+4xy+y^2\right)}{xy\left(x^2-y^2\right)}\)

  \(=\frac{x^4-2x^2y+xy^2+3x^2y+4xy^2+y^3}{xy\left(x^2-y^2\right)}\)

\(=\frac{x^4+x^2y+5xy^2+y^3}{xy\left(x^2-y^2\right)}=\frac{x^2\left(x^2+y\right)+y^2\left(5x+y\right)}{xy\left(x^2-y^2\right)}\)

a) A = 2 a 3   +   6 ab 2 .                  b) B = ( x   –   y   –   z ) 3 .