a/ \(=x^2+2x-7x-14=x\left(x+2\right)-7\left(x+2\right)=\left(x-7\right)\left(x+2\right)\)
b/ \(=15-3x=3\left(5-x\right)\)
c/ \(=x^2-3xy-4xy+12y^2=x\left(x-3y\right)-4y\left(x-3y\right)=\left(x-4y\right)\left(x-3y\right)\)
d/ \(=x^3-2x^2+x+2x^2-4x+2=x\left(x^2-2x+1\right)+2\left(x^2-2x+1\right)=\left(x+2\right)\left(x-1\right)^2\)