由题意可知:x=g(y)与y=f(x)互为反函数,故:g′(y)= 1 f′(x) g″(y)= d dy g′(y)= d dy 1 f′(x) = d dx 1 f′(x) dx dy =? f″(x) f′(x)2 1 f′(x) =? f″(x) f′(x)3