x2-3(a+1)x+2(3a+1)

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x2-3(a+1)x+2(3a+1)

x2-3(a+1)x+2(3a+1)
x2-3(a+1)x+2(3a+1)

x2-3(a+1)x+2(3a+1)
x2-3(a+1)x+2(3a+1)
=(x-2)(x-3a-1)
当2>3a+1 即a

x2-3(a+1)x+2(3a+1)<=0
[x-(3a+1)][x-2]<=0
根据3a+1和2的大小展开讨论:
1、 3a+1>=2
a>=1/3
2<=x<=3a+1
2、3a+1<2
a<1/3
3a+1<=x<=2

x2-3(a+1)x+2(3a+1)<=0
即(x-2)(x-3a-1)<=0
x<=2时, x>3a+1 , 即: 3a+1x>2时, x<=3a+1 , 即: 2

用判别试去算,很容易的,在去算下a的一元两次方程

分解成(-x+2)×(-x+3a+1)就行了.在用穿线法分类讨论求解