a) 5x² -20

=  5(x² -4)

=5 (x² -2²)

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

b) 16 - (x+y)²

=4² -(x+y)²

= (4-x-y)(4+x+y) 

a, \(5\left(x^2-4\right)=5\left(x-2\right)\left(x+2\right)\)

b, \(16-\left(x+y\right)^2=\left(4-x-y\right)\left(4+x+y\right)\)

mấy bài này áp dụng hđt là được nhé 

5x² - 20 = 5( x² - 4 ) = 5( x - 2 )( x + 2 )

16 - ( x + y )² = 4² - ( x + y ) = ( 4 - x - y )( 4 + x + y ) 

5 x² - 5xy+2x−2y = 2x ( x - y) + 2( x - y) = 2( x + 1)( x - y)

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

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

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

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

\(5x-5y-xy+y^2=\left(5x-5y\right)-\left(xy-y^2\right)=5\left(x-y\right)-y\left(x-y\right)=\left(x-y\right)\left(5-y\right)\)

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

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

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

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

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

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

5x³ - 20

= 5.(x³ - 4)

#

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

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

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

\(y^2+3y\)

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

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

a) \(x^2-xy+x-y\)

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

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

b) \(x^2+5x+6\)

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

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

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

\(2xy-x^2-y^2+16\)

\(=16-\left(x-y\right)^2\)

\(=\left(4-x+y\right)\left(4+x-y\right)\)

\(3x\left(x-2\right)-x+2+5x\left(x-2\right)=\left(x-2\right)\left(8x-1\right)\)

\(3x\left(x-2\right)-x+2+5x\left(x-2\right)=3x\left(x-2\right)-\left(x-2\right)+5x\left(x-2\right)=\left(x-2\right)\left(3x=1+5x\right)=\left(x-2\right)\left(8x-1\right)\)