1)（x²+y²-z²）²-4x²y²
=[(x²+y²-z²）+2xy][(x²+y²-z²）-2xy]
=[(x+y)²-z²][(x-y)²-z²]
=(x+y+z)(x+y-z)(x-y+z)(x-y-z)
2).x²-3x+6xy+9y²-9y
=(x+3y)²-3(x+3y)
=(x+3y)[(x+3y)-3]
=(x+3y)(x+3y-3)