1.A

2.C

3.B

4.C

a

c

b

c

(x-1)y^2-4(x-1)y

\(1,\\ a,=4\left(x-2\right)^2+y\left(x-2\right)=\left(4x-8+y\right)\left(x-2\right)\\ b,=3a^2\left(x-y\right)+ab\left(x-y\right)=a\left(3a+b\right)\left(x-y\right)\\ 2,\\ a,=\left(x-y\right)\left[x\left(x-y\right)^2-y-y^2\right]\\ =\left(x-y\right)\left(x^3-2x^2y+xy^2-y-y^2\right)\\ b,=2ax^2\left(x+3\right)+6a\left(x+3\right)\\ =2a\left(x^2+3\right)\left(x+3\right)\\ 3,\\ a,=xy\left(x-y\right)-3\left(x-y\right)=\left(xy-3\right)\left(x-y\right)\\ b,Sửa:3ax^2+3bx^2+ax+bx+5a+5b\\ =3x^2\left(a+b\right)+x\left(a+b\right)+5\left(a+b\right)\\ =\left(3x^2+x+5\right)\left(a+b\right)\\ 4,\\ A=\left(b+3\right)\left(a-b\right)\\ A=\left(1997+3\right)\left(2003-1997\right)=2000\cdot6=12000\\ 5,\\ a,\Leftrightarrow\left(x-2017\right)\left(8x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=2017\\x=\dfrac{1}{4}\end{matrix}\right.\\ b,\Leftrightarrow\left(x-1\right)\left(x^2-16\right)=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=4\\x=-4\end{matrix}\right.\)

\(1,=x\left(x^2-2x+1-y^2\right)=x\left[\left(x-1\right)^2-y^2\right]=x\left(x-y-1\right)\left(x+y-1\right)\\ 2,=\left(x+y\right)^3\\ 3,=\left(2y-z\right)\left(4x+7y\right)\\ 4,=\left(x+2\right)^2\\ 5,Sửa:x\left(x-2\right)-x+2=0\\ \Leftrightarrow\left(x-2\right)\left(x-1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)

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

\(y^2-\left(x^2-2x+1\right)=y^2-\left(x-1\right)^2=\left(y-x+1\right).\left(y+x-1\right)\)

     y\(^2\) - ( x\(^2\) - 2x + 1 )

⇔ y\(^2\) - ( x - 1 )\(^2\)

⇔ ( y - x - 1 ) ( y + x - 1 )

b: \(=\dfrac{12\left(y-z\right)^4+3\left(y-z\right)^5}{6\left(y-z\right)^2}=2\left(y-z\right)^2+\dfrac{1}{2}\left(y-z\right)^3\)

\(x^4-2x^2-144x-1295=\left(x+5\right)\left(x-7\right)\left(x^2+2x+37\right)\)

1295^2 - 144 = 1677025 - 144 = 1676881 

(x+y) ^ 4 = (x+y) x (x+y) x (x+y) x (x+y) = 4(x+y) + x^4 + y^4 = 4 + 4 + 4 = 4 x 3 = 12 

\(\dfrac{1}{x-y}-\dfrac{1}{x+y}+\dfrac{2x}{\left(x-y\right)\left(x+y\right)}\\ \dfrac{x+y}{\left(x-y\right)\left(x+y\right)}-\dfrac{x-y}{\left(x-y\right)\left(x+y\right)}+\dfrac{2x}{\left(x-y\right)\left(x+y\right)}\\ \dfrac{x+y-x+y+2x}{\left(x-y\right)\left(x+y\right)}\\ \dfrac{2x+2y}{\left(x-y\right)\left(x+y\right)}\\ \dfrac{2}{x-y}\)

\(\dfrac{1}{x-y}+\dfrac{1}{x+y}+\dfrac{2x}{x^2-y^2}=\dfrac{x+y}{\left(x-y\right)\left(x+y\right)}+\dfrac{x-y}{\left(x-y\right)\left(x+y\right)}+\dfrac{2x}{\left(x-y\right)\left(x+y\right)}=\dfrac{4x}{\left(x-y\right)\left(x+y\right)}\)

\(\dfrac{1}{x-y}-\dfrac{1}{x+y}+\dfrac{2x}{x^2-y^2}\\ =\dfrac{x+y}{x-y}-\dfrac{x-y}{x+y}+\dfrac{2x}{\left(x-y\right)\left(x+y\right)}\\ =\dfrac{2x+2y}{\left(x-y\right)\left(x+y\right)}\\ =\dfrac{2\left(x+y\right)}{\left(x-y\right)\left(x+y\right)}\\ =\dfrac{2}{x-y}\)

\(R=\left(2x\right)^2-2.2x.y+y^2\\ =\left(2x-y\right)^2\\ =>D\)

\(a,x^2-x-y^2+y\\=(x^2-y^2)-(x-y)\\=(x-y)(x+y)-(x-y)\\=(x-y)(x+y-1)\\---\\b,x^2+2x+2z-z^2\\=(x^2-z^2)+(2x+2z)\\=(x-z)(x+z)+2(x+z)\\=(x+z)(x-z+2)\\\text{#}Toru\)

Lời giải:

a. $x^2-x-y^2+y=(x^2-y^2)-(x-y)=(x-y)(x+y)-(x-y)=(x-y)(x+y-1)$

b. $x^2+2x+2z-z^2=(x^2+2x+1)-(z^2-2z+1)=(x+1)^2-(z-1)^2$

$=(x+1-z+1)(x+1+z-1)=(x-z+2)(x+z)$

\(a,x^2-x-y^2+y\\ =\left(x^2-y^2\right)-\left(x-y\right)\\ =\left(x-y\right)\left(x+y\right)-\left(x-y\right)\\ =\left(x-y\right)\left(x+y-1\right)\\ ---\\ b,x^2+2x+2z-z^2\\ =\left(x^2+2x+1\right)-\left(z^2-2z+1\right)\\ =\left(x+1\right)^2-\left(z-1\right)^2\\ =\left[\left(x+1\right)+\left(z-1\right)\right].\left[\left(x+1\right)-\left(z-1\right)\right]\\ =\left(x+z\right)\left(x-z+2\right)\)