1) \(3x^2-9=3\left(x^2-3\right)\)
2) \(\dfrac{1}{2}x^2-2y^2\)
\(=\dfrac{1}{2}\left(x^2-4y^2\right)\)
\(=\dfrac{1}{2}\left(x-2y\right)\left(x +2y\right)\)
3) \(3x^2-12y^2\)
\(=3\left(x^2-4y^2\right)\)
\(=3\left(x-2y\right)\left(x+2y\right)\)
4) \(\dfrac{1}{3}x^2y^2-3x^2\)
\(=\dfrac{1}{3}x^2\left(y^2-9\right)\)
\(=\dfrac{1}{3}x^2\left(y-3\right)\left(y+3\right)\)
#Toru