问题 填空题
已知x=4-
2
,则分式
x4-6x3-2x2+18x+23
x2-8x+15
=______.
答案

∵当x=4-

2
时,x2-8x+15=(x-3)(x-5)=(1-
2
)(-1-
2
)=1,

x4-6x3-2x2+18x+23
x2-8x+15

=x4-6x3-2x2+18x+23

=x2(x2-8x+15)+2x(x2-8x+15)-(x2-8x+15)-20x+38

=x2+2x-1-20x+38

=x2-18x+37

=(x2-8x+15)-10x+22

=1-10x+22

=23-10x,

∴当x=4-

2
时,原式=23-10(4-
2
)=10
2
-17.

故答案为:10

2
-17.

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