[[1]]
原式=(a³-2a²)+(3a²-6a)+(6a-12)
=a²(a-2)+3a(a-2)+6(a-2)
=(a-2)(a²+3a+6)
[[2]]
原式=[(x^4)+2x³]-(2x³+4x²)-(2x²+4x)-(3x+6)
=x³(x+2)-2x²(x+2)-2x(x+2)-3(x+2)
=(x+2)(x³-2x²-2x-3)
而x³-2x²-2x-3
=(x³-3x²)+(x²-3x)+(x-3)
=x²(x-3)+x(x-3)+(x-3)
=(x-3)(x²+x+1)
∴原式=(x+2)(x-3)(x²+x+1)