先化简，再选一个你喜欢的值代入求值．4-xx-2÷(x+2-12x-2)．

Question

先化简，再选一个你喜欢的值代入求值．(4-x)/(x-2)÷(x+2-(12)/(x-2))．

Answer 1

原式=(4-x)/(x-2)÷[((x+2)(x-2))/(x-2)-(12)/(x-2)]
=(4-x)/(x-2)÷(x2-4-12)/(x-2)
=(4-x)/(x-2)•(x-2)/(x2-16)
=(4-x)/(x2-16)
=(4-x)/((x+4)(x-4))
=-(1)/(x+4)．
令x=1，原式及计算过程中的分式的分母均不为0，
当x=1时，原式=-(1)/(1+4)=-(1)/(5)．