先化简再求值 (x-4)/(x-1)除以(x+1-15/(x-1)),其中x=5根号2-4
问题描述：
先化简再求值 (x-4)/(x-1)除以(x+1-15/(x-1)),其中x=5根号2-4
答
原式=(x-4)/(x-1)÷(x²-1-15)/(x-1)
=(x-4)/(x-1)÷(x²-16)/(x-1)
=(x-4)/(x-1)*(x-1)/(x+4)(x-4)
=1/(x+4)
=1/(5√2-4+4)
=√2/10