Question

因式分解！！

a³+2a²-12a+15
x³-21x+20

Answer 1

您好：

a³+2a²-12a+15
=a³+5a²-3a²-15a+3a+15
=a²(a+5)-3a(a+5)+3(a+5)
=(a+5)(a²-3a+3)

x³+1-21x-21
=(x+1)(x²-x+1)-21(x+1)
=(x+1)(x²-x-20)
=(x+1)(x+4)(x-5)

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追问

)(a²-3a+3) 是不是还可以继续分啊

追答

没法分了

Answer 2

a³+2a²-12a+15
=a³+5a²-3a²-15a+3a+15
=a²(a+5)-3a(a+5)+3(a+5)
=(a+5)(a²-3a+3)

x³-21x+20
=x³-x²+x²-x-20x+20
=x²(x-1)+x(x-1)-20(x-1)
=(x-1)(x²+x-20)
=(x-1)(x-4)(x+5)