1) x²+2xy+y²-49=(x+y)²-7²=(x+y-7)(x+y+7)
2) a²-9b²+6bc-c² = a²-(9b²-6bc+c²)= a²-(3b-c)²=(a-3b+c)(a+3b-c)
3)
4) a³+8-a²-2a=(a+2)(a²-2a+4)-a(a+2)=(a+2)(a²-2a+4-a)=(a+2)(a²-3a+4)
5)
6)
7) a²+2ab+b²-c²+4cd-4d² =(a+b)²-(c-2d)² =(a+b+c-2d)(a+b-c+2d)
8)
9) (x-y)(x+y)+2(x+2y)-3=x²-y²+2x+4y-3=x²+2x-y²+4y-3=x(x+2)-y(y-4)-3