I think this should read (1) -3x2-13xy-4y2 or (2) -3x2+13xy-4y2
(1)
-(3x2+13xy+4y2)=-(3x2+12xy+xy+4y2)=
-(3x(x+4y)+y(x+4y))=
-(3x+y)(x+4y).
(2)
-(3x2-13xy+4y2)=-(3x2-12xy-xy+4y2)=
-(3x(x-4y)-y(x-4y))=
-(3x-y)(x-4y), which can be written:
(y-3x)(x-4y).