问题
填空题
已知x=4-
|
答案
∵当x=4-
时,x2-8x+15=(x-3)(x-5)=(1-2
)(-1-2
)=1,2
∴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-
时,原式=23-10(4-2
)=102
-17.2
故答案为:10
-17.2