^2 + 4xy - 16 + 4y^2 
= x^2 + 4xy + 4y^2 - 4^2 
= (x + 2y)^2 - 4^2 
= (x + 2y - 4)(x + 2y + 4) 
2x^2-5xy-3y^2 
= 2^x + xy - 6xy - 3y^2 
= x(2x + y) - 3y(2x + y) 
= (2x + y)(x - 3y)

mình chưa hiểu

Lời giải:

$A=x^2-8xy+15y^2=x^2-3xy-(5xy-15y^2)$

$=x(x-3y)-5y(x-3y)=(x-3y)(x-5y)$

$B=2x^2-5xy+2y^2=(2x^2-4xy)-(xy-2y^2)$

$=2x(x-2y)-y(x-2y)=(2x-y)(x-2y)$

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

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

1) \(2\left(x-1\right)^3-\left(x-1\right)=\left(x-1\right)\left(2\left(x-1\right)^2-1\right)\)

2) \(y\left(x-2y\right)^2+xy^2\left(2y-x\right)=\left(2y-x\right)\left(2\left(2y-x\right)+1\right)=\left(2y-x\right)\left(4y-2x+1\right)\)

3) \(xy\left(x+y\right)-x-y=xy\left(x+y\right)-\left(x+y\right)=\left(x+y\right)\left(xy-1\right)\) (xem lại đề sửa -2x thành -x mới đúng)

4) \(xy\left(x-3y\right)-2x+6y=xy\left(x-3y\right)-2\left(x-3y\right)=\left(x-3y\right)\left(xy-2\right)\)

x²+3x+3y+xy

=x(x+3)+y(3+x)

=(x+3)(x+y)

     x² + 3x + 3y + xy

=   ( x² + xy) + ( 3x + 3y)

= x( x + y) + 3 ( x + y)

= ( x + y) ( x + 3) 

=(x+y)(x+3)

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

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

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

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

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

\(xy^3-5x^2\)

\(=x\cdot y^3-x\cdot5x\)

\(=x\left(y^3-5x\right)\)

\(y^2+3y\)

\(=y\cdot y+y\cdot3\)

\(=y\left(y+3\right)\)

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

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

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

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

\(=xy\left(x-y-1\right)\left(x+y+1\right)\)

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

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

\(=3\left(x+y\right)-x\left(x+y\right)\)

\(=\left(3-x\right)\left(x+y\right)\)