Revisiting definition of derivative
Let us revisit the definition of the derivative and try to see it in a different way. Let , then If we write and , then and where represents the change in and represents the change in . The notation or should not be confused with a product. The Greek capital letter is read as 'delta' and is used in place of the letter 'd'. The choice of the letter is convenient as represents the change or difference in values and so is the change or difference in . Thus we have