1.      2(x-2)

2.       x(x+1)

3     2ab(a-2)

4          (y+1)(x-y)

5       (x+y)(ax+ay-1)

Bạn nên tách ra thành từng câu hỏi thì hơn

Chứ dài quá 

.

a)\(9x^2y^2+15x^2y-21xy^2\)

=\(3xy\left(3xy+5x-7y\right)\)

b)\(3x^2\left(x+1\right)-2\left(x+1\right)\)

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

c)\(4x^2\left(x-2y\right)-20x\left(2y-x\right)\)

=\(4x^2\left(x-2y\right)+20x\left(x-2y\right)\)

=\(\left(4x^2+20x\right)\left(x-2y\right)\)

=\(4x\left(x+5\right)\left(x-2y\right)\)

a. ta có :

\(9x^2y^2+15x^2y-21xy^2=3xy\left[3xy+5x-7y\right]\)

b.\(3x^2\left(x+1\right)-2\left(x+1\right)=\left(x+1\right)\left[3x^2-2\right]\)

\(4x^2\left(x-2y\right)+20x\left(x-2y\right)=\left(x-2y\right)\left(4x^2+20x\right)=4x\left(x-2y\right)\left(x+5\right)\)

GTNN của D là 10 nha

Ta có \(\hept{\begin{cases}\left(5x-3\right)^2\ge0\\4\left|5x-3\right|\ge0\end{cases}\forall x}\)

\(\Rightarrow\left(5x-3\right)^2-4\left|5x-3\right|+14\ge14\)

\(\Rightarrow D\ge14\)

Dấu "=" xảy ra <=> 5x-3=0 <=> x=3/5

\(\left(a+1\right)^2-\left(a-1\right)^2-3\left(a+1\right)\left(a-1\right)\)

\(=a^2+2a+1-a^2+2a-1-3\left(a^2-1\right)\)

\(=4a-3a^2+1\)

ai n hanh 1 k

a) \(\left(x^2+x\right)^2-2\left(x^2+x\right)-15=\left(x^2+x\right)^2-5\left(x^2+x\right)+3\left(x^2+x\right)-15\)

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

b) \(x^2+2xy+y^2-x-y-12=\left(x+y\right)^2-\left(x+y\right)-12=\left(x+y\right)^2-4\left(x+y\right)+3\left(x+y\right)-12\)

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

c) \(\left(x^2+x+1\right)\left(x^2+x+2\right)-12=\left(x^2+x\right)^2+3\left(x^2+x\right)+2-12=\left(x^2+x\right)^2+3\left(x^2+x\right)-10\)

\(=\left(x^2+x\right)^2+5\left(x^2+x\right)-2\left(x^2+x\right)-10=\left(x^2+x-2\right)\left(x^2+x+5\right)\)

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

d) \(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24=\left[\left(x+2\right)\left(x+5\right)\right]\left[\left(x+3\right)\left(x+4\right)\right]-24\)

\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)

\(=\left(x^2+7x+11\right)^2-1-24\)

\(=\left(x^2+7x+6\right)\left(x^2+7x+16\right)\)

5x+20-x^2-4x=0

<=>x+20-x^2=0

<=>x(x+1)=-20

<=>x=4

5x+20-x^2-4x=0

x = 5 

nha nha

day la x-1 phan 2 nha