a-maths~!!!!!

let k= (4+x)/(4-x)

4k - kx= 4 + x

4(k-1 ) = x( k+1)

x/4 = (k-1)/ (k+1) = 1 - 2/( k+1)

so, lim( x->4) x /4 = 1 = 1- 2/( k+1)

as there is no solution of k , lim( x->4) (4+x)/(4-x) is no defined .

2008-07-01 19:22:59 補充：
可用上極限and下極限來做,

check下 lim(x-> +4 ) f(x) = lim(x-> -4) f(x) ???

Put x=4 into the fraction, which is not in the form of 0/0, infinity/0, or 0/infinity, which implies that the limit does not exists