x^4+4y^4
=x^4+4y^4+4x²y²-4x²y²
=(x²+2y²)²-4x²y²
=(x²+2y²+2xy)(x²+2y²-2xy)
X³-3X²-2X+2
=(x³+1)-(3x²+2x-1)
=(x+1)(x²-x+1)-(x+1)(3x-1)
=(x+1)(x²-x+1-3x+1)
=(x+1)(x²-4x+2)
16X²-9Y²+32X+16
=(4x+4)²-9y²
=(4x+4-3y)(4x+4+3y)
X^4+X²Y²+Y^4
=x^4+y^4+2x²y²-x²y²
=(x²+y²)²-x²y²
=(x²+y²+xy)(x²+y²-xy)