4x^4-2x^2+1
=4x^4+4x²+1-6x²
=(2x²+1)-(√6x)²
=(2x²+√6x+1)(2x²-√6x+1)
x²+4xy-y²
=x²+4xy+4y²-5y²
=(x+2y)²-(√5y)²
=(x+2y+√5y)(x+2y-√5y)
=[x+(2+√5)y][x+(2-√5)y]