Question

用配方法因式分解怎么做啊！！这两个例题

x^2+6x+8
2x^2-4x-9
一个是平方前面没有系数，另一个有。。。

Answer 1

x²+6x+8
=x²+6x+9-1
=(x+3)²-1
=(x+3+1)(x+3-1)
=(x+4)(x+2)

2x²-4x-9
=2x²-4x+2-11
=2(x-1)²-11
=2[(x-1)²-22]
=2(x-1+√22)(x-1-√22)