化简/X+3/X+1,其中x=3-根号2的值

题目

化简/X+3/X+1,其中x=3-根号2的值

答案

x=3-√2
(x-1-8/(x+1))/[(x+3)/(x+1)]
=((x-1)(x+1)-8)/(x+1)/[(x+3)/(x+1)]
=(x²-1-8)/(x+3)
=(x²-9)/(x+3)
=(x²-3²)/(x+3)
=(x+3)(x-3)/(x+3)
=x-3=3-√2-3=-√2