x²-3xy+2y²-2x+3y+1
=(x-y)(x-2y)-(2x-3y)+1
=(x-y-1)(x-2y-1)
x⁴+4
=(x²）²+2²+4x²-4x²
=（x²+2）²-（2x）²
=（x²+2x+2）（x²-2x+2）