4xy - x² + 9 - 4y²

= -(x² - 4xy + 4y² - 9)

= -[(x² - 4xy + 4y²) - 3²]

= -[(x - 2y)² - 3²]

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

\(\left(x+2y-4\right)\left(x+2y+4\right)\)

1.A

2.C

3.B

4.C

a

c

b

c

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

b) x2y + 4xy + 4y – y3

= y(x2 + 4x + 4 - y2)

= y[(x2 + 4x + 4) - y2]

= y[(x + 2)2 - y2]

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

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

x^2- 4y^2 + 4xy

= x^2 + 4xy - 4y^2

=x^2 + 2x2y - (2y)^2

= ( x - 2y )^2

 x² - 4y² + 4xy = x² + 4xy - 4y² = - (x² - 4xy + 4y²) = - ((x² - 2x.2y + (2y)²)

= - ( x - 2y)²

\(x^2-25-4xy+4y^2\)

\(=\left(x^2-4xy+4y^2\right)-25\)

\(=\left[x^2-2\cdot x\cdot2y+\left(2y\right)^2\right]-25\)

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

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