✔ 最佳答案
1.
P(x)=x^3-4x^2-4x-5
可試x=1,-1,5,-5
最後試到
P(5)=125-100-20-5=0
x-5 is a factor
by division,
P(x)=(x-5)(x^2+x+1)
(x^2+x+1)cannot be factorized
(b^2-4ac<0)
P(x)=(x-5)(x^2+x+1)
2.
P(x)=x^3-7x^2+7x-6
可試x=1,-1,2,-2,3,-3,6,-6
最後試到
P(6)=216-252+42-6=0
x-6 is a factor
by division,
P(x)=(x-6)(x^2-x+1)
(x^2-x+1)cannot be factorized
(b^2-4ac<0)
P(x)=(x-6)(x^2-x+1)
3.
P(x)=x^3-4x+15
可試x=1,-1,3,-3,5,-5,15,-15
最後試到
P(-3)=-27+12+15=0
x+3 is a factor
by division,
P(x)=(x+3)(x^2-3x+5)
(x^2-3x+5)cannot be factorized
(b^2-4ac<0)
P(x)=(x+3)(x^2-3x+5)