1. y^2-y+2y-2=y(y-1)+2(y-1)=(y-1)(y+2)
2. x^2-25y^2=(x-5y)(x+5y)
3.ab^2-2ab+a=ab^2-ab-ab+a=a(b^2-2b+1)=a(b-1)^2
