因式分解的简单应用 (23 12:14:38)

1.x2-6x=-9
x^2-6x+9=0
(x-3)^2=0
x=3
2.(x+2)2=(2x+1)2
[(x+2)+(2x+1)][(x+2)-(2x+1)]=0
(3x+3)(-x+1)=0
3(x+1)(1-x)=0
x1=-1,x2=1
3.9(x+3)2=(2x-5)2
[3(x+3)+(2x-5)][3(x+3)-(2x-5)]=0
(5x+4)(x+14)=0
x1=-4/5,x2=-14
4.若a2+a-3=0,求a4+2a3-a-1的值
a4+2a3-a-1
=(a^4+a^3-3a^2)+(a^3+a^2-3a)+(2a^2+2a-6)+5
=a^2(a^2+a-3)+a(a^2+a-3)+2(a^2+a-3)+5
=5