先化简，再求值：（3x-1-1x+1）÷xx2-1，其中x=6．

Question

先化简，再求值：（ (3)/(x-1) -(1)/(x+1) ） ÷(x)/(x2 -1) ，其中x=6．

Answer 1

原式= (3(x+1)-(x-1))/((x+1)(x-1)) ÷ (x)/((x+1)(x-1))
= (2(x+2))/((x+1)(x-1)) • ((x+1)(x-1))/(x)
= (2(x+2))/(x) ，
当x=6时，原式= (2×(6+2))/(6) = (8)/(3) ．