Chapter 0 Preface 3) Diferential of a function(函数的微分) If f() has its derivative at point x, then f()dx is its differential at that point dy= f(x)dx Differential of the function Differential of the variable So f(r) dy is also called differential quotient(微商)Chapter 1Chapter 1 Measurment Chapter 0 Preface 3) Differential of a function (函数的微分) If f(x) has its derivative at point x, then f ’(x)dx is its differential at that point. dy = f '(x)dx dx Differential of the function Differential of the variable  So f ’(x) is also called differential quotient (微商) dx dy =