(*)\(\left(x-7\right)\left(x-5\right)\left(x-4\right)\left(x-2\right)-72\)
\(=\left[\left(x-7\right)\left(x-2\right)\right]\left[\left(x-4\right)\left(x-5\right)\right]-72\)
\(=\left(x^2-9x+14\right)\left(x^2-9x+20\right)-72\)
\(=y\left(y+6\right)-72\) với \(y=x^2-9x+14\)
\(=y^2+6y-72\)
\(=y^2-6y+12y-72\)
\(=y\left(y-6\right)+12\left(y-6\right)\)
\(=\left(y-6\right)\left(y+12\right)\)