1) 3a(2 -b) +45(b -2) =3a(2 -b) -45(2 -b)=(2 -b)(3a -45) = 3(2 -b)(a -15)
2) x² -y² -x -y =(x -y)(x +y) -(x+y) =(x +y)(x -y -1)
3) 60+6ab -3ab -12a =60 +3ab -12a =3(20 +ab -4a)
4) x(y -5) -y(5 -y) =x(y -5) + y(y -5) =(y -5)(x +y)
5) (3a²-a+2) +(-3a²+3a -1) - (a² -1) =3a² -a +2 -3a² +3a -1 -a² +1 =2a -a² +2