a, \(x^3-2x^2+x=x\left(x^2-2x+1\right)=x\left(x-1\right)^2\)
b, \(x\left(x+3y\right)-5x-15y=x\left(x+3\right)-5\left(x+3y\right)=\left(x-5\right)\left(x+3y\right)\)
c, \(x^2-y^2+2020x+2020y=\left(x+y\right)\left(x-y\right)+2020\left(x+y\right)=\left(x-y+2020\right)\left(x+y\right)\)


