How to define the vector division has been plagued by people. We redefine the fraction , where represents an arbitrary vector, and extend it to discuss the differentiability and integrability of two or more variables function. In this book we directly exploit the definition of derivatives for two variable functions. According to our research, we discover various forms of the Mean Value(Vector) Theorems and the Fundamental Theorems of Calculus for multiple integrals. This book adds a new understanding to the field of multi-variable calculus and thus helps those who are working in the subject.We divide our research into three sections in this book. In Chapter 1, by defining the line derivector and plane derivector, we explain the chain rule for differentiation of multi-variables function, differential and the mean vector theorem. In Chapter 2, we illustrate the formula derivation of i) line derivector for a 2-variable function, ii) line derivatives for 2-variable functi
