Derivatives

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If c < 0 then | x | (non-negative) is always greater than c.
Hence the question is not applicable for c < 0
If c = 0,
f(x) = { 1/|x| if x <> 0
f(x) = { b if x = 0
If f(0) is continuous at x = c = 0, then b approaches infinity which also means the question does not have good meaning
If c > 0, in order for f’(c) to exist,
(1) f’(c-) = f’(c+)
a = -1/c^2
(2) f(x) is continuous at x = c
f(c-) = ac + b
f(c+) = 1/c
ac + b = 1/c
(-1/c^2)c + b = 1/c
b = 2/c

2010-01-24 23:37:51 補充：
你對一對你的計法好嗎?要不然給我電郵分享你的計算方法.讓我看看為甚麼會有差別.