1: =x^2-2*x*2y+4y^2
=(x-2y)^2
2: 9x^2-y^2=(3x-y)(3x+y)
5: x^3-8=(x-2)(x^2+2x+4)
4: =x^2-(y-2)^2
=(x-y+2)(x+y-2)
7: 8x^3+12x^2+6x+1=(2x+1)^3
14: =x^3-3x^2+3x-1-1
=(x-1)^3-1
=(x-1-1)(x^2-2x+1+x-1+1)
=(x-2)(x^2-x+1)
15: =x^3+x^2-4x^2-4x+7x+7
=(x+1)(x^2-4x+7)
16: =2x^3-x^2-2x^2+x+2x-1
=(2x-1)(x^2-x+1)