\(A=\left(x^2+2x\right)^2-2x^2-4x-3\)
\(A=\left(x^2+2x\right)^2-2\left(x^2+2x\right)-3\)
Đặt \(t=x^2+2x\), ta có:
\(A=t^2-2t-3\)
\(A=t^2-3t+t-3\)
\(A=t\left(t-3\right)+\left(t-3\right)\)
\(A=\left(t-3\right)\left(t+1\right)\)
Thay \(t=x^2+2x\), ta có:
\(A=\left(x^2+2x-3\right)\left(x^2+2x+1\right)\)
\(A=\left(x-1\right)\left(x+3\right)\left(x+1\right)^2\)