HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 66

Differentiating There are different approaches that can be taken to differentiating, most of which are best done in the SYMB view of the Function aplet. The syntax of the differentiation function is: ∂X ( function) where function is defined in terms of X. The function can be already defined in the SYMB view of the Function aplet as shown in functions F1(X) and F2(X) in the screen shot above. Alternatively it can be directly entered into the brackets as shown in function F3(X). The ∂ symbol most easily obtained by pressing the key labeled d/dx . It can also be found in the MATH menu. One point to remember is that if you use this function in the HOME view you may not receive the result you expect. If you try this yourself your result will probably not be the same as that shown right. The reason for this is that the result you see is the derivative of x2 − x evaluated at whatever value of x happens to be currently in memory. This can be seen more clearly if we store a specific value into the memory X beforehand. In the example shown right, the answer of 3 is the value of the derivative 2x −1 at the value of x = 2. But what of algebraic differentiation? It is possible but not very convenient to do this in the HOME view using a "formal variable" of S1. The drawback of this is simply the awkwardness of having to work with S1's rather than with X's. 66