a) \(3x^2-4y+4x-3y^2\)
\(=\left(3x^2-3y^2\right)-\left(4y-4x\right)\)
\(=3\left(x^2-y^2\right)-4\left(x+y\right)\)
\(=3\left(x-y\right)\left(x+y\right)-4\left(x+y\right)\)
\(=\left(x+y\right)\left(3\left(x-y\right)-4\right)\)
\(=\left(x+y\right)\left(3x-3y-4\right)\)