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

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

\(= x 2 + 2 x y + y 2 + x 2 − 2 x y + y 2 − 2 x 2 = 2 y 2\)

Ta có: \(A=\left(x-y-1\right)^3-\left(x-y+1\right)^3+6\left(x-y\right)^2\)

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

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

\(=-6\left(x-y\right)^2+6\left(x-y\right)^2-2\)

=-2

\(=\dfrac{1}{y-x}\cdot x^3\cdot\left(x-y\right)=-x^3\)

A

lộn

4*x*y câu C bạn nhé 

\(=\left(\dfrac{39}{4}:\dfrac{26}{5}+\dfrac{17}{5}\cdot\dfrac{55}{24}\right):\dfrac{-25}{16}\)

=-464/75

\(2,=x^2-3^2=\left(x-3\right)\left(x+3\right)\\ 3,=\left(x+y-x+y\right)\left(x+y+x-y\right)\\ =2y\cdot2x=4xy\)

x^2-9=x^2-3^2=(x+3)(x-3)
(x+y)^2-(x-y)^2=(x+y+x-y)(x+y-x-y)=2x

x²-3²=(x-3)(x+3)

(x+y)²-(x-y)²=(x+y-x+y)(x+y+x-y)=2y⋅2x=4xy

mọi người ơi,tùy chọn bên dưới là kết quả bên trên nha!

mọi người giúp với :!!!!!

6) \(\sqrt{\left(2-\sqrt{5}\right)^2}=\left|2-\sqrt{5}\right|=\sqrt{5}-2\)  =>Chọn 2

7) \(\sqrt{4\left(a-2\right)^2}=2\left|a-2\right|=2\left(2-a\right)\)( do \(a\le2\)) => Chọn 3

8) Để \(\sqrt{4+a^2}\) thì \(4+a^2\ge0\left(đúng\forall a\right)\) => Chọn 1

9) \(x^2-7=\left(x-\sqrt{7}\right)\left(x+\sqrt{7}\right)\)  => Chọn 3

10) \(\sqrt{\left(-25\right)\left(-64\right)}=\sqrt{25.64}=\sqrt{25}.\sqrt{64}=5.8=40\)=> Chọn 3

\(A=\left(x+2\right)\left(x^2-2x+4\right)-8\)

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

\(=x^3\)

D  nhá!!

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

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