a) \(x^2+4x-12\)
\(=x^2-2x+6x-12\)
\(=x\left(x-2\right)+6\left(x-2\right)\)
\(=\left(x-2\right)\left(x+6\right)\)
b) \(3x^2-8x+4\)
\(=3x^2-2x-6x+4\)
\(=x\left(3x-2\right)-2\left(3x-2\right)\)
\(=\left(3x-2\right)\left(x-2\right)\)
c) \(4x^2-4x-3\)
\(=4x^2-2x+6x-3\)
\(=2x\left(2x-1\right)+3\left(2x-1\right)\)
\(=\left(2x-1\right)\left(2x+3\right)\)
d) \(6x^2-11x+3\)
\(=6x^2-2x-9x+3\)
\(=2x\left(3x-1\right)-3\left(3x-1\right)\)
\(=\left(3x-1\right)\left(2x-3\right)\)