1) x2- 3x - 6x +18
= (x2- 3x )-(6x -18 )
= x(x-3)- 6(x-3)
= (x-6)(x-3)
\(2,x^2-3x-54\)
\(=x^2-9x+6x-54\)
\(=x\left(x-9\right)+6\left(x-9\right)\)
\(=\left(x+6\right)\left(x-9\right)\)
\(3,20x^2+7x-6\)
\(=20x^2-8x+15x-6\)
\(=4x\left(5x-2\right)+3\left(5x-2\right)\)
\(=\left(4x+3\right)\left(5x-2\right)\)