先化简,再求值:[X-1-8/(X-1)]÷(x+3)/(x+1) 其中x=3-根号2
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解决时间 2021-12-25 11:34
- 提问者网友:难遇难求
- 2021-12-25 07:58
,,,x-1和8不是一个整体啦
最佳答案
- 五星知识达人网友:迷人又混蛋
- 2021-12-25 09:20
[x-1-8/(X-1)]÷(x+3)/(x+1)
=[(x-1)^2-8]/(x-1)*(x+1)/(x+3)
=[(x-1)^2-8]*(x+1)/[(x-1)(x+3)]
=[(x-1+2√2)(x-1-2√2](x+1)/[(x-1)(x+3)]
=[(3-√2-1+2√2)(3-√2-1-2√2](3-√2+1)/[(3-√2-1)(3-√2+3)]
=(2+√2)(2-3√2)(4-√2)/[(2-√2)(6-√2)]
=-14√2/[14-8√2]
=-(56+49√2)/17 .
=[(x-1)^2-8]/(x-1)*(x+1)/(x+3)
=[(x-1)^2-8]*(x+1)/[(x-1)(x+3)]
=[(x-1+2√2)(x-1-2√2](x+1)/[(x-1)(x+3)]
=[(3-√2-1+2√2)(3-√2-1-2√2](3-√2+1)/[(3-√2-1)(3-√2+3)]
=(2+√2)(2-3√2)(4-√2)/[(2-√2)(6-√2)]
=-14√2/[14-8√2]
=-(56+49√2)/17 .
全部回答
- 1楼网友:逐風
- 2021-12-25 10:46
[(x-1)-8/(x+1)]除以(x+3)/(x+1)
=(x²-1-8)/(x+1)×(x+1)/(x+3)
=(x²-9)/(x+3)
=(x+3)(x-3)/(x+3)
=x-3
代入x=3-√2
原式=3-√2-3
=-√2
希望能帮到你o(∩_∩)o
- 2楼网友:有你哪都是故乡
- 2021-12-25 10:14
=[X-1-8/(X-1)]*(x+1) ÷(x+3)
={[(X-1)^2-8] / (X-1)}*(x+1)÷(x+3)
=[(X-1)*2-8]*(x+1)/(X-1)*(x+3)
=(X^2-2x-7)*(X+1) / (X^2+2x-3)
把x=3-根号2 代入式子
=(9-6根号2 +2-6+2根号2-7)*(3-根号2+1) / (9-6根号2 +2+6-2根号2-3)
=(-2-4根号)*(2-根号2)/ (14-8根号2)
= -(1+根号2)*(2-根号2) / (7-4根号2)
=-(2+根号2-2)/ 7-4根号2
=4-根号2/7
不知道有没算对
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