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

\(=5x(x-2)-(x-2)\)

\(=(x-2)(5x-1)\)

\(\Rightarrow5x\left(x-2\right)-\left(x-2\right)\)

\(\Rightarrow\left(x-2\right)\left(5x-1\right)\)

\(\Rightarrow\left\{{}\begin{matrix}x-2=0\\5x-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=2\\x=\dfrac{1}{5}\end{matrix}\right.\)

\(15x^2-34x+15\)

\(=15x^2-25x-9x+15\)

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

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

\(\Rightarrow\left(x^2+2x\right)^2+9\left(x^2+2x\right)+20=\left(x^2+2x\right)^2+4\left(x^2+2x\right)+5\cdot\left(x^2+2x\right)+20=\left(x^2+2x\right)\left(x^2+2x+4\right)+5\left(x^2+2x+4\right)=\left(x^2+2x+4\right)\left(x^2+2x+5\right)\)

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

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

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

(x2+2x)+9x2+18x+20

=(x2+2x)+9(x2+2x)+20

Đặt t=x2+2x đc:

t+9t+20=10t+20=10(t+2)

Thay t=x2+2x vào đc:

10(x2+2x+2)

\(=\left(x^2+2x\right)^2+9\left(x^2+2x\right)+20\)

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

\(18x^2-36xy+18x^2-72z^2\)

\(=36x^2-36xy-72z^2\)

\(=36\left(x^2-xy-2z^2\right)\)

A bằng 2x(4x^2-12x+9)

A bằng 2x(2x-3)^2

\(4\left(x^2+15x+50\right)\left(x^2+18x+72\right)-3x^2\)

\(=4\left(x+5\right)\left(x+10\right)\left(x+12\right)\left(x+6\right)-3x^2\)

\(=4\left(x^2+17x+60\right)\left(x^2+16x+60\right)-3x^2\)

\(=4\left(x+60\right)^2+132x\left(x+60\right)+1088x^2-3x^2\)

\(=4\left(x+60\right)^2+132x\left(x+60\right)+1085x^2\)

\(=4\left(x+60\right)^2+62x\left(x+60\right)+70x\left(x+60\right)+1085x^2\)

\(=2\left(x+60\right)\left[2\left(x+60\right)+31x\right]+35x\left[2\left(x+60\right)+31x\right]\)

\(=\left(33x+120\right)\left(2x+120+35x\right)\)

\(=3\left(11x+40\right)\left(37x+120\right)\)