a/ \(=2xy+6x^2-y^2-3xy=2x\left(y+3x\right)-y\left(y+3x\right)=\left(2x-y\right)\left(y+3x\right)\)
b/ \(=2x^2+5xy+y^2\)
c/ \(=-4y^2+6xy-4xy+6x^2=-2y\left(2y-3x\right)-2x\left(2y-3x\right)=\left(-2y-2x\right)\left(2y-3x\right)=-2\left(y+x\right)\left(2y-3x\right)\)
d/ \(=-4y^2-2xy+4xy+2x^2=-2y\left(2y+x\right)+2x\left(2y+x\right)=\left(-2y+2x\right)\left(2y+x\right)=-2\left(y-x\right)\left(2y+x\right)\)