1)5a²-4a-5b²+4b
=5(a²-b²)-4(a-b)
=5(a+b)(a-b)-4(a-b)
=(a-b)(5a+5b-4)
2)3a-ax-3b+bx
=3a-3b-ax+bx
=3(a-b)-x(a-b)
=(a-b)(3-x)
3)6a²-35xy+10ay-21ax
=6a²+10ay-35xy-21ax
=2a(3a+5y)-7x(5y+3a)
=(2a-7x)(3a+5y)
4)x²+2x-y²+2y
=x²-y²+2x+2y
=(x+y)(x-y)+2(x+y)
=(x+y)(x-y+2)
5)3a²-2b+6ab-a
=3a²-a-2b+6ab
=a(3a-1)+2b(-1+3a)
=(a+2b)(3a-1)
6)1-x²-y²+2xy
=1-(x²-2xy+y²)
=1-(x-y)²
=(1+x-y)(1-x+y)