因式分解:
(1)9-4a2=________________
(2)-15x3y2+10x2y4-20x4y3=__________________
(3)a2-5ab+6b2=__________________
(4)-m2+4mn-4n2=________________________
(1)9-4a2=________________
(2)-15x3y2+10x2y4-20x4y3=__________________
(3)a2-5ab+6b2=__________________
(4)-m2+4mn-4n2=________________________