7)
`4x^2-12x+9-y^2`
`=(2x-3)^2-y^2`
`=(2x-3-y)(2x-3+y)`
8)
`16x^2-4y^2+4y-1`
`=16x^2-(4y^2-4y+1)`
`=16x^2-(2y-1)^2`
`=(4x-2y+1)(4x+2y-1)`
9)
`25-x^2-12x-36`
`=25-(x^2+12x+36)`
`=25-(x+6)^2`
`=(5-x-6)(5+x+6)`
`=(-1-x)(x+11)`
10)
`x^2-9-5(x+3)`
`=(x+3)(x-3)-5(x+3)`
`=(x+3)(x-3-5)`
`=(x+3)(x-8)`
11)
`5(x-y)+y^2-xy`
`=5(x-y)+y(y-x)`
`=5(x-y)-y(x-y)`
`=(5-y)(x-y)`
12)
`14a^2b^3-35ab^2+7a^2b^2`
`=7ab^2(2ab-5+a)`
13)
`6a^2b^3-30ab^2+12a^2b^2`
`=6ab^2(ab-5+2a)`
