1.1/2p^2-2pq
=p(p/2-2q)
2.-3x+6x^2-3x^3
=-3x(x^2+2x+1)
=-3x(x+1)^2
3.a^2（a-3)-a+3
=a^2(a-3)-(a-3)
=(a^2-1)(a-3)
=(a+1)(a-1)(a-3)
4.2xy-x^2-y^2+1
=-(x^2-2xy+y^2)+1
=1-(x-y)^2
=(1-x+y)(1+x-y)