3x²-xy²+3x-y²
=x(3x-y²)+(3x-y²)
=(3x-y²)(x+1)
3x^4+6x-9
=3(x^4+2x-3)
=3(x²+3)(x²-1)
=3(x²+3)(x-1)(x+1)
x^4-3x²-4
=(x²-4)(x²+1)
=(x-2)(x+2)(x²+1)
4b²c²-（b²+c²-a²）²
=(2bc-b²-c²+a²)(2bc+b²+c²-a²)
=[a²-(b²-2bc+c²)][(2bc+b²+c²)-a²]
=[a²-(b-c)²][(b+c)²-a²]
=(a-b+c)(a+b-c)(b+c-a)(b+c+a)