是a³+3a²-4
=(a³-1)+3(a²-1)
=(a-1)(a²+a+1)+3(a-1)(a+1)
=(a-1)(a²+a+1+3a+3)
=(a-1)(a²+4a+4)
=(a-1)(a+2)²
因式分解x^3+3a^2-4是a³+3a²-4
是a³+3a²-4
=(a³-1)+3(a²-1)
=(a-1)(a²+a+1)+3(a-1)(a+1)
=(a-1)(a²+a+1+3a+3)
=(a-1)(a²+4a+4)
=(a-1)(a+2)²